Proceedings Volume 4841

Instrument Design and Performance for Optical/Infrared Ground-based Telescopes

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Proceedings Volume 4841

Instrument Design and Performance for Optical/Infrared Ground-based Telescopes

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Volume Details

Date Published: 7 March 2003
Contents: 10 Sessions, 173 Papers, 0 Presentations
Conference: Astronomical Telescopes and Instrumentation 2002
Volume Number: 4841

Table of Contents

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Table of Contents

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  • Overview Session I
  • Overview Session II
  • Poster Session A
  • Optical Detectors and Cameras
  • IR Detectors and Cameras
  • IR Spectrographs I/Cameras I
  • IR Detectors and Cameras
  • Optical Spectrograph I
  • Optical Detectors and Cameras
  • IR Detectors and Cameras
  • IR Spectrographs I/Cameras I
  • Poster Session B
  • IR Spectrogaphs II
  • Optical Spectrograph I
  • IR Spectrographs I/Cameras I
  • Optical Spectrograph I
  • Optical Spectrograph II
  • Poster Session B
Overview Session I
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Instrumentation at the Keck Observatory
Current instruments and plans for new instruments for the W.M. Keck Observatory are reviewed on behalf of the Keck Science Steering Committee. Much has happened in the last two years. Both 10-meter telescopes have been in full operation for some time and each has a significant complement of instruments. Adaptive optics systems are functioning on both telescopes, the Keck II laser guide star system has been tested, and the Keck Interferometer has achieved first fringes. The existing LRIS spectrograph on Keck I has been upgraded to provide a UV/blue optimized channel and two new instruments have been delivered within the past year, namely, DEIMOS, a multi-object spectrograph and NIRC2, a diffraction-limited IR camera. A near-infrared integral field unit spectrometer for AO is currently under development, as is a CCD detector upgrade for the existing HIRES spectrograph. Future plans include detector upgrades for LRIS-R, and a powerful wide-field near-IR multi-object spectrometer.
Overview Session II
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Overview of the Subaru telescope instrumentation
Takuya Yamashita, Tetsuo Nishimura
The Subaru Telescope has seven first generation optical and infrared instruments now being handed-over from the instrument teams to the observatory and being offered for its open use. We describe brief history of the telescope project and overview of the instrumentation program. Brief status of the Individual instruments is given separately. Exchanging focal plane and instruments is important for such multi-purpose telescope and the effectiveness of the system with the Subaru Telescope is discussed. Finally, current challenges of the program and future plans are summarized.
Gemini Observatory's facility instrument program
Douglas A. Simons, Robert Nolan, Manuel Lazo, et al.
This is the fourth in a series of SPIE papers that chronicle the accomplishments, challenges, and evolution of Gemini's instrumentation program. For the first time we are pleased to report about progress made on instruments being fabricated as well as results with completed instruments, now steadily producing world-class scientific results at the Gemini Observatory. With the steady arrival of new facility class instruments, we anticipate phasing out our reliance on visitor instruments, which have enabled our early scientific capabilities at both Gemini-N and Gemini-S. Currently two facility class instruments are operational and six more are due in roughly a year, hence commissioning all of these instruments in Hawaii and Chile will doubtless be an enormous task for the staff at Gemini in the near future.
Overview of instrumentation for the large binocular telescope
An overview of the 3 facility instruments and 2 strategic interferometric instruments under construction for the Large Binocular Telescope is presented. Planned optical instrumentation includes the Large Binocular Camera (LBC), a pair of wide-field (25' x 25') UB/VRI optimized mosaic CCD imagers at the prime focus, and the MultiObject Double Spectrograph (MODS), a pair of dual-beam blue-red optimized longslit spectrographs mounted at the straight-through F/15 Gregorian focus incorporating multiple slit masks for multi-object spectroscopy over a 5' field and spectral resolutions of 2000-8000. Infrared instrumentation includes the LBT Near-IR Spectroscopic Utility with Camera and Integral Field Unit for Extragalactic Research (LUCIFER), a modular near-infrared (0.9-2.5 μm) imager and spectrograph pair mounted at a bent interior focal station and designed for seeing limited (FOV: 4' x 4') and diffraction limited (FOV: 0.5' x 0.5') imaging and longslit spectroscopy, seeing limited multiobject spectroscopy utilizing cooled slit masks, and optional diffraction limited integral field spectroscopy. Strategic instruments under development for the remaining two combined focal stations include an interferometric cryogenic beam combiner with NIR and thermal IR instruments for Fizeau imaging and nulling interferometry and an optical bench beam combiner with visible and NIR imagers utilizing in the future multi-conjugate adaptive optics for angular resolutions as high as 5 mas at a wavelength of 0.5 μm. The availability of all these instruments mounted simultaneously on the LBT permits flexible scheduling and improved operational support.
Performance of the facility instruments on the Hobby-Eberly telescope
The Hobby-Eberly Telescope (HET) is a revolutionary large telescope of 9.2 meter aperture, located in West Texas at McDonald Observatory. Early scientific operations started on October 8, 1999. The HET operates with a fixed segmented primary and has a tracker which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. As of two years ago, the HET was taking science data but the image quality and primary mirror stability were far from specifications. We established the HET Completion Project to identify and fix these problems, and here we describe the current performance of the HET relative to its goals, focusing on progress made in the past two years. The first phase of HET instrumentation includes three facility instruments: the Low Resolution Spectrograph (LRS) and High Resolution Spectrograph (HRS), which are in operation, and the Medium Resolution Spectrograph (MRS), which will be commissioned in the summer and autumn. The current status of the instruments is described in detail with performance measures.
Instrumentation for the California Extremely Large Telescope
The Phase A study for the California Extremely Large Telescope (CELT) Project has recently been completed. As part of this exercise a working group was set-up to evolve instrumentation strategies matched to the scientific case for the CELT facility. We report here on the proposed initial instrument suite which includes not only massively multiplexed seeing-limited multi-object spectroscopy but also on plans for wide-field adaptive optics fed integral-field spectroscopy and imaging at, or approaching, CELT's diffraction limit.
Poster Session A
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Design status of WFCAM: a wide-field camera for the UK Infrared Telescope
An update on the design status of the UKIRT Wide Field Camera (WFCAM) is presented. WFCAM is a wide field infrared camera for the UK Infrared Telescope, designed to produce large scale infrared surveys. The complete system consists of a new IR camera with integral autoguider and a new tip/tilt secondary mirror unit. WFCAM is being designed and built by a team at the UK Astronomy Technology Centre in Edinburgh, supported by the Joint Astronomy Centre in Hawaii. The camera uses a novel quasi-Schmidt camera type design, with the camera mounted above the UKIRT primary mirror. The optical system operates over 0.7 - 2.4 μm and has a large corrected field of view of 0.9° diameter. The focal plane is sparsely populated with 4 2K x 2K Rockwell HAWAII-2 MCT array detectors, giving a pixel scale of 0.4 arcsec/pixel. A separate autoguider CCD is integrated into the focal plane unit. Parallel detector controllers are used, one for each of the four IR arrays and a fifth for the autoguider CCD.
Megacam: the new Canada-France-Hawaii Telescope wide-field imaging camera
Olivier Boulade, Xavier Charlot, P. Abbon, et al.
MegaCam is an imaging camera with a 1 square degree field of view for the new prime focus of the 3.6 meter Canada-France-Hawaii Telescope. This instrument will mainly be used for large deep surveys ranging from a few to several thousands of square degrees in sky coverage and from 24 to 28.5 in magnitude. The camera is built around a CCD mosaic approximately 30 cm square, made of 40 large thinned CCD devices for a total of 20 K x 18 K pixels. It uses a custom CCD controller, a closed cycle cryocooler based on a pulse tube, a 1 m diameter half-disk as a shutter, a juke-box for the selection of the filters, and programmable logic controllers and fieldbus network to control the different subsystems. The instrument was delivered to the observatory on June 10, 2002 and first light is scheduled in early October 2002.
Design and results of the fast timing photo-polarimeter OPTIMA
Gottfried Kanbach, Stefan Kellner, Fritz Z. Schrey, et al.
A high-speed photometer, "OPTIMA" short for Optical Pulsar Timing Analyzer, has been designed as a sensitive, portable detector to observe optical pulsars and other highly variable sources. The detector contains eight fiber fed avalanche photodiode single photon counters, a GPS timing receiver, a CCD camera for target acquisition and a computerized control unit. The central fibers are configured as a hexagonal bundle around the target fiber, while one fiber is located at a distance of ~1' as a monitor for the night sky background. Recently a rotating polarization filter and a 4-color prism spectrograph have been added to the system as optional equipment. Since January 1999 OPTIMA has been used on different telescopes to measure detailed lightcurves and polarization of the Crab Pulsar, in a search for optical emission from the Geminga pulsar, and for the timing of cataclysmic variables and X-ray transients.
GOHSS: A MOS fiber-fed multi-echelle spectrograph in the near infrared (0.9-1.8 um)
We describe the current status and technical aspects of the GOHSS (Galileo OH Subtracted Spectrograph) project. Here we point out the most critical items and how we have implemented innovative technical solutions to fulfill the compelling requirements imposed by both the optical tolerances and the demands of a high sensitivity. In particular we examine the camera lens mechanics realized in ultra low expansion quartz; the refrigerator system; the IR array mount realized in an unconventional way; the effort put in procuring optical devices with quite large efficiencies. We are also developing the data reduction package along with the instrument simulator: the optimized procedures and the results on the visibility function of galaxies are given as well. Currently the instrument is in the integration phase at the laboratories of the Astronomical Observatory of Rome and the commissioning phase at the telescope is expected to start at the beginning of year 2003.
MIRSI: a mid-infrared spectrometer and imager
Lynne K. Deutsch, Joseph L. Hora, Joseph D. Adams, et al.
MIRSI (Mid-InfraRed Spectrometer and Imager) is a mid-infrared camera system recently completed at Boston University that has both spectroscopic and imaging capabilities. MIRSI is uniquely suited for studies of young stellar objects and star formation, planetary and protoplanetary nebulae, starburst galaxies, and solar system objects such as planets, asteroids, and comets. The camera utilizes a 320 x 240 Si:As Impurity Band Conduction (IBC) array developed for ground-based astronomy by Raytheon/SBRC. For observations at the Infrared Telescope Facility (IRTF), MIRSI offers a large field of view (1.6 arcmin x 1.2 arcmin) with a pixel scale of 0.3 arcsec, diffraction-limited spatial resolution, complete spectral coverage over the 8-14 μm and 17-26 μm atmospheric windows for both imaging (discrete filters and circular variable filter) and spectroscopy (10 and 20 μm grisms), and high sensitivity (expected one-sigma point source sensitivities of 5 and 20 mJy at 10 and 20 μm, respectively, for on-source integration time of 30 seconds). MIRSI successfully achieved first light at the Mt. Lemmon Observing Facility (MLOF) in December 2001, and will have its first observing run at the IRTF in November 2002. We present details of the system hardware and software and results from first light observations.
TIMMI2, ESO's Thermal Infrared Multimode Instrument: technical description and some scientific results
Hans-Ulrich Kaufl, Michael F. Sterzik, Ralf Siebenmorgen, et al.
TIMMI2 ESO's 2nd generation Thermal Infrared Multimode Instrument had astronomical first light in October 2000 at the 3.6 m telescope on La Silla, Chile. Since February 2001 it is in regular use, both by visiting astronomers and in service mode, typically one third of the total telescope time. Using a Raytheon 240 x 320 pixel As:Si-BIB detector allows imaging and grism spectroscopy between 5 and 24 μm. TIMMI2 has also a linear polarimetry mode. We will give a description of the instrument from technical to operational aspects. Because of the substantial gain in sensitivity as compared to previous generation instruments a new set of infrared calibration standards has been constructed. The instrument and telescope are subject of an ongoing sensitivity monitoring program enabling to improve the sensitivity while allowing to spot the development of problems immediately. For stellar objects the sensitivity 10 σ in 1 hour of telescope time is in the range of 15 - 30 mJy. TIMMI2 at the telescope shows negligible flexure (≤ 0.2") while having basically diffraction limited performance for λ ≥ 8 μm.
Characterization of DRS Technologies' 256x256 mid-infrared arrays for VISIR
Philippe Galdemard, Florence Garnier, Patrick Mulet, et al.
Two DRS Technologies (formerly Boeing Sensors and Electronic Systems) 256 x 256 Si:As Blocked Impurity Band (BIB) focal plane arrays have been rigorously tested in 2001 and 2002 in the IR laboratory of CEA/Saclay/Service d'Astrophysique. These mid-IR arrays equip VISIR, the mid-infrared imager and spectrometer made under contract by CEA (France) and ASTRON (Netherlands) for the ESO Very Large Telescope. Measurement results crucial to the project appliction are presented. These include array dark current versus temperature and the Background Limited noise Performance (BLIP) capability. Operational optimization for astronomical use is also discussed in this paper.
Integration time dependence of tunnel noise and energy resolution of superconducting tunnel junctions
Peter Verhoeve, Roland H. den Hartog, Alex G. Kozorezov, et al.
Superconducting tunnel junctions (STJs) offer the capability of photon counting with intrinsic energy resolving power. This resolving power is ultimately limited by the variance on the number of charge carriers generated in the photon absorption process (Fano limit) and the variance on the number of tunnelled charge carriers (tunnel limit). In addition, the performance can be degraded by electronic noise related to the read-out of the devices and by spatial non-uniformities in the response across the detector area. The present generation of our Ta-Al STJs is such that their spectroscopic performance in the UV/visible is limited by tunnel noise. This noise contribution is usually considered a device constant, (which may only vary marginally with bias conditions) and evaluated for infinite integration time. It can be shown, however, that the tunnel noise contribution is strongly time dependent and can be reduced by almost an order of magnitude for a properly chosen integration time. In this paper we present the experimental demonstration and numerical simulations of this time dependence on a series of Ta-Al STJs with different pulse decay times. The experimental results are in qualitative agreement with the simulations, but do not quite achieve the predicted performance. For the optimum configuration, an effective tunnel noise contribution of ~70% of the conventional tunnel limit is found.
Suprime Cam: Subaru prime focus camera
The Suprime-Cam is a CCD camera which is attached to the prime focus of the Subaru Telescope. Ten MIT/LL CCDs are tiled with small gaps to realize large field of view (34' x 27') with 0.2 arcsec sampling. This makes the Suprime-Cam very powerful and unique instrument among 8-10m class telescopes. We present basic design, key techniques, current status and performance of the Suprime-Cam. We also mention ongoing survey programs with the Suprime-Cam, followed by future upgrade plans of the camera.
LIRIS (Long-slit Intermediate Resolution Infrared Spectrograph): assembly integration and verification
LIRIS is a near-infrared (0.9 - 2.4 microns) intermediate resolution spectrograph (R = 1000-3000) conceived as a common user instrument for the (WHT) at the Observatorio del Roque de los Muchachos (ORM) La Palma. LIRIS is now being assembled, integrated and virified at the Instituto Astrofisico de Canarias (IAC). LIRIS will have imaging, long-slit and multi-object spectroscopy working modes. Coronography and polarimetry capabilities will eventually be added. Image capability will allow easy target acquisition.
Improved performances and capabilities of the Cooled Mid-Infrared Camera and Spectrometer (COMICS) for the Subaru Telescope
Yoshiko Kataza Okamoto, Hirokazu Kataza, Takuya Yamashita, et al.
COMICS is an observatory and mid-infrared instrument for the 8.2 m Subaru Telescope. It is designed for imaging and spectroscopic observations in the N- (8-13 micron) and Q-bands (16-25 micron) atmospheric windows. The design and very preliminary performances at the first light observations in December 1999 were reported at the SPIE meeting in 2000. We describe here the improved performances of COMICS and capability of high spectral resolution spectrocopy which became available from December 2001. We will also briefly report preliminary scientific results.
Precision cryogenic mechanisms for the Michelle mid-infrared spectrograph
David Montgomery, John Murray
The UKATC has recently delivered and commissioned the Michelle mid-IR spectrograph on UKIRT. This instrument has a variety of precision vacuum-cryogenic mechanisms that utilize technology developed over a number of years at the UKATC in instruments such as IRCAM, CGS4, SCUBA, GMOS and UIST. In these applications it is critical that the mechanisms operate reliably and with a high degree of precision. In most cases the mechanisms support optical elements that must be rigidly held in place when the instrument is tilted during observations on the telescope. This paper describes the level of performance achieved with the Michelle mechanisms and the critical elements of their design.
The Redstar3 array controller: embedding Linux and PCs as a DSP replacement
The design of the Redstar3 array control system including operational requirements and performance is presented. The architecture is intended to support next generation large format infrared/optical arrays and mosaics by using a new scalable approach that takes advantage of commercially available electronics. Specifically, an approach of using a combination of high speed fiber links, networked PCs and Linux to replace the previous generation of VME based DSPs will be discussed in detail. The design will be used to control HAWAII-2RG (1-4.9μm 2Kx2K HgCdTe), Aladdin II and III (1-5 μm 1Kx1K InSb) arrays in facility class instruments for Gemini, NSO and IRTF. It is also intended to be the platform for high count curvature correction, waveform sense and control for adaptive optics.
The L band high-speed guide camera with nanomesh resonant dichroic
TEXES, the Texas Echelon Cross Echelle Spectrograph, is an ideal instrument to study molecular clouds at a spectral resolving power of 100,000 between 5 and 25 μm. In many molecular clouds, high extinction often means that no visible stars are available for off-axis guiding. At a resolving power of 100,000, only the very brightest sources can be observed while guiding on the power in the dispersed IR spectra. We present the design of a high-speed on-axis guider for TEXES operating at 3.65 μm, a wavelength outside the spectrometer operating band where many of the target sources are still detectable for imaging. We use a new technology gold nanomesh resonant IR filter/mirror from EDTEK, that transmits 3.65 μm light to the guide detector with a peak transmittance of 60% while reflecting light from 5 μm long-ward with 98% efficiency to the dispersing elements in the spectrograph. A PC controls clocking patterns for the CRC-463 detector from Raytheon Infrared Operations and the analog to digital conversion of signals with a 14 bit A/D card. Image centroiding is done in software and then offsets are sent to the telescope for pointing adjustments or tip-tilt corrections when a tip-tilt secondary is available. This system is a prototype designed to test the feasibility of a similar guider for EXES, the Echelon Cross Echelle Spectrograph, mounted on SOFIA, the Stratospheric Observatory for Infrared Astronomy.
The CCD imaging systems for DEIMOS
Christopher A.F. Wright, Robert I. Kibrick, Barry Alcott, et al.
The DEep Imaging Multi-Object Spectrograph (DEIMOS) images with an 8K x 8K science mosaic composed of eight 2K x 4K MIT/Lincoln Lab (MIT/LL) CCDs. It also incorporates two 1200 x 600 Orbit Semiconductor CCDs for active, close-loop flexure compensation. The science mosaic CCD controller system reads out all eight science CCDs in 40 seconds while maintaining the low noise floor of the MIT/Lincoln Lab CCDs. The flexure compensation (FC) CCD controller reads out the FC CCDs several times per minute during science mosaic exposures. The science mosaic CCD controller and the FC CCD controller are located on the electronics ring of DEIMOS. Both the MIT/Lincoln Lab CCDs and the Orbit flexure compensation CCDs and their associated cabling and printed circuit boards are housed together in the same detector vessel that is approximately 10 feet away from the electronics ring. Each CCD controller has a modular hardware design and is based on the San Diego State University (SDSU) Generation 2 (SDSU-2) CCD controller. Provisions have been made to the SDSU-2 video board to accommodate external CCD preamplifiers that are located at the detector vessel. Additional circuitry has been incorporated in the CCD controllers to allow the readback of all clocks and bias voltages for up to eight CCDs, to allow up to 10 temperature monitor and control points of the mosaic, and to allow full-time monitoring of power supplies and proper power supply sequencing. Software control features of the CCD controllers are: software selection between multiple mosaic readout modes, readout speeds, selectable gains, ramped parallel clocks to eliminate spurious charge on the CCDs, constant temperature monitoring and control of each CCD within the mosaic, proper sequencing of the bias voltages of the CCD output MOSFETs, and anti-blooming operation of the science mosaic. We cover both the hardware and software highlights of both of these CCD controller systems as well as their respective performance.
Status of the EMIR optical system
EMIR is a intermediate resolution near infrared (1.0 - 2.5 microns) multiobject spectrograph with image capabilities, to be mounted on the Gran Telescopio Canarias (GTC). EMIR is being built by a consortium of Spanish, French and British institutions, led by the Instituto de Astrofísica de Canarias. EMIR is being funded by GRANTECAN and the Plan Nacional de Astronomía y Astrofísica (National Plan for Astronomy and Astrophysics, Spain) as one of the first common user instruments for the GTC. The instrument shall deliver images and spectra from a large FOV (6x6 arcmin in imaging mode, and 6x4 arcmin in multislit spectroscopic mode). Due to the telescope image scale (1 arcmin = 52 mm) and the spectral resolution required (around 4000), one of the major challenges of the instrument is the optical design and the manufacture. The detailed optical design and its expected performance will be presented. In particular the main risk areas will be identified and our risk control strategy will be outlined.
Design and testing of external structures for the UIST instrument
The UIST instrument is a 1-5μm Imager Spectrometer for the UKIRT telescope. The instrument has a high spatial resolution, and is designed to critically sample image sizes of 0.24arcsec. The instrument weighs 750kg and measures approximately 1100x1000x700mm. The flexure specification for the instrument is to maintain the image at the slit within 10% of the narrowest slit width, which is 44μm wide. However combined flexure of the instrument and its supporting structure is expected to be many times more than this. To meet the UIST flexure requirements we propose use of an instrument specific component in the telescope pointing model, to correct for repeatable flexure. Two designs for mounting regimes are presented, together with flexure test results and a discussion of the use of a simple pointing correction. The first, flexible, truss design did not meet requirements and was replaced with a rigid truss system. The paper describes some lessons learned during the development of the UIST mounting scheme, which can be applied in other instrument designs.
Calibration of VISIR: the VLT mid-infrared imager/spectrometer
Arnaud J. Claret, Pierre-Olivier Lagage, Eric Pantin, et al.
Since the beginning of the VISIR project, the calibration aspects have been taken into account as an integral part of the design. In order to provide the user and the archive with high quality and well-controlled data, it is mandatory to have, during the routine observation phase, all calibration observations as part of the instrument set-up activities and as part of the actual Astronomical Observing Template. We propose here to review the calibration of VISIR observations. After a description of the various hardware tools which have been introduced for calibration purposes (warm calibration unit, distortion grid, pupil imaging optics, wavelength calibration modules), we will present the calibrations in four astronomical categories (spatial resolution, photometry, astrometry and wavelength calibration). Cross-calibrations between the Imager and Spectrometer subsystems will also be addressed.
A wide-field infrared camera for the Observatoire du mont Mégantic
A wide-field near-infrared (0.8 - 2.4 μm) camera for the 1.6 m telescope of the Observatoire du mont Megantic (OMM), is currently under construction at the Universite de Montreal. The field of view is 30' × 30' and will have very little distortion. The optics comprise 8 spherical cryogenic lenses. The instrument features two filter wheels with provision for 10 filters including broad band I, z, J, H, K and other narrow-band filters. The camera is based on a 2048 × 2048 HgCdTe Hawaii-2 detector driven by a 3--output SDSU-II controller operating at ~250 kHz.
Performance of HAWAII-2 FPAs for multi-object infrared camera and spectrograph
Yuka Katsuno, Takashi Ichikawa, Ken'ichiro Asai, et al.
We report on the results of the performance tests of the HAWAII-2 FPAs for Multi-Object Infra-Red Camera and Spectrograph (MOIRCS). MOIRCS provides wide-field imaging mode (4'x7' F.O.V.) and multi-object spectroscopy mode for the wavelength range from 0.85 to 2.5 μm. To achieve the wide field-of-view with the high angular resolution, we use two 2048 x 2048 HgCdTe FPAs, HAWAII-2. We have made performance tests of both the engineering-grade and the science-grade HAWAII-2 arrays. Array performances such as stability of bias frames, read noise and dark current are evaluated at the operating temperature of 78K. In addition, we search for the optimum well depth, readout speed by changing bias voltages. We have finished tests of the engineering-grade array and the performance of our science-grade arrays is under investigation.
The University of Hawaii Wide-Field Imager
Klaus-Werner Hodapp, Andrew J. Pickles, Gerard A. Luppino, et al.
The University of Hawaii Wide-Field Imager (UHWFI) is a focal compressor designed to project the full half-degree field of the UH 2.2m telescope onto the refurbished 8K×8K CCD camera. The optics use Ohara glasses and are mounted in an oil-filled cell to minimize light losses and ghost images from the large number of internal surfaces. The UHWFI is equipped with a six-position filter wheel and a rotating sector shutter, both driven by stepper motors. The instrument is currently in the design phase and will be commissioned early in 2003.
SOAR Optical Imager
The SOAR Optical Imager (SOI) is the commissioning instrument for the 4.2-m SOAR telescope, which is sited on Cerro Pachón, and due for first light in April 2003. It is being built at Cerro Tololo Inter-American Observatory, and is one of a suite of first-light instruments being provided by the four SOAR partners (NOAO, Brazil, University of North Carolina, Michigan State University). The instrument is designed to produce precision photometry and to fully exploit the expected superb image quality of the SOAR telescope, over a 6x6 arcmin field. Design goals include maintaining high throughput down to the atmospheric cut-off, and close reproduction of photometric passbands throughout 310-1050nm. The focal plane consists of a two-CCD mosaic of 2Kx4K Lincoln Labs CCDs, following an atmospheric dispersion corrector, focal reducer, and tip-tilt sensor. Control and data handling are within the LabVIEW-Linux environment used throughout the SOAR Project.
Calibration of CONICA static aberrations by phase diversity
Markus Hartung, Amandine Blanc, Thierry Fusco, et al.
CONICA is the first AO equipped multimode near infrared camera which saw first light at the VLT in the end of 2001. A technique will be described to benefit of the AO system NAOS to correct not only for atmospheric turbulence but also for the internal optical aberrations of the high resolution camera. The aberrant optical components in the light path of CONICA are outside of the AO loop and therefore no self-acting correction is possible. Independently of the AO wave front sensor, a separate measurement of these minor aberrations using a method called phase diversity allows to predict for the variety of camera configurations the corresponding aberrations. They are quantified by sets of Zernike coefficients which are rendered to the adaptive optics. This technique turns out to be very flexible and results into a further improvement of the optical overall performance.
Optical design of MOIRCS
We describe an optical design process and image performance evaluations for Multi-Object near-InfraRed Camera and Spectrograph (MOIRCS). MOIRCS is a near-infrared imager and multi-object spectrograph under construction for the Subaru Telescope. MOIRCS provides direct imaging of 4' x 7' F.O.V. with a pixel scale of 0.12". MOIRCS also provides low-resolution multi-object spectroscopy with grisms and cooled multi-slit masks on the Cassegrain focal plane. CaF2, BaF2, ZnSe, and Fused Silica are used as the lens materials. They have high transmission in the near-infrared wavelength. During the design process, we find that a triplet with an achromatic doublet and a ZnSe singlet shows good performance for chromatic aberration. Therefore, we design our optics on the basis of the triplet with ZnSe. The designed optics shows good performances. Ensquared energy within 2 pixel square is more than 85% over the entire wavelength range and F.O.V. We do not need refocusing with the change of observed wavelengths because chromatic aberration is as small as 100 μm by the triplet with ZnSe over the entire wavelength range from 0.85 to 2.5 μm. Lateral chromatic aberration of 15 μm is less than 1 pixel size. Detailed tolerance analysis is done with possible manufacturing and aligning errors considered. The result shows that designed performances will be kept with a probability of 80% with reasonable tolerances. Ghost analysis is also done over entire F.O.V. and we find a ghost image of 13 magnitude fainter than original image that is not significant for our purpose. Therefore, we conclude that we can obtain enough performances with designed optics.
NIFS concentric integral field unit
John Hart, Peter J. McGregor, Gabe J. Bloxham
The Gemini Near-infrared Integral Field Spectrograph (NIFS) will be used with the ALTAIR adaptive optics system on Gemini North. NIFS uses a reflective, concentric, integral field unit (IFU) to reformat its focal plane. The concentric IFU design integrates the IFU with the spectrograph collimator to form a dedicated IFU instrument. The IFU channels are identical and fanned about a single axis passing through the image slicer. The spherical optical surfaces of the spectrograph collimator are all concentric and centered on this fanning axis. The grating is also located on the fanning axis, and the system is arranged to produce coincident pupil images at the grating. In this way, each channel of the IFU performs as if it is on-axis. This avoids complications due to off-axis angles that are intrinsic to other reflective IFU designs.
KALI Camera: mid-infrared camera for the Keck interferometer nuller
Michelle J. Creech-Eakman, James D. Moore, Dean L. Palmer, et al.
We present a brief overview of the KALI Camera, the mid-infrared camera for the Keck Interferometer Nulling Project, built at the Jet Propulsion Laboratory. The instrument utilizes mainly transmissive optics in four identical beam paths to spatially and spectrally filter, polarize, spectrally disperse and image the incoming 7-14 micron light from the four outputs of the Keck Nulling Beam Combiner onto a custom Boeing/DRS High Flux 128 X 128 BIB array. The electronics use a combination of JPL and Wallace Instruments boards to interface the array readout with the existing real-time control system of the Keck Interferometer. The cryogenic dewar, built by IR Laboratories, uses liquid nitrogen and liquid helium to cool the optics and the array, and includes six externally motorized mechanisms for aperture and pinhole control, focus, and optical component selection. The instrument will be assembled and tested through the summer of 2002, and is planned to be deployed as part of the Keck Interferometer Nulling experiment in 2003.
Cryogenic engineering for OMEGA2000: design and performance
Harald Baumeister, Peter Bizenberger, Coryn A. L. Bayler-Jones, et al.
Omega2000 is a prime focus near infrared (NIR) wide-field camera for the 3.5 meter telescope at Calar Alto/Spain. Having a large field of view and an excellent optical quality, the instrument is particularly designed for survey observations. A cryogenic four lens focal reducer delivers a 15.4 x 15.4 arcminute field of view (FOV) with a pixel scale of 0.45"/pixel. The lenses are made of various optical materials, including CaF2 and BaF2 with diameters of up to 150 mm. They must be specially mounted to survive cooling and to follow the tight tolerances (± 0.05 mm for lens centricity and ± 30 arcsec for lens tilt) required by the optical design. For a wide range of observing applications, a filter mechanism can hold up to 17 filters of 3 inch diameter in 3 filter wheels. For exact and reproducible filter positions, a mechanical locking mechanism has been developed which also improves the cool-down performance of the filter wheels and filters. This mechanism allows a minimum distance of about 3 mm between the filter wheels. A Rockwell HAWAII-2 FPA is used to cover the wavelength range from 0.85 μm to 2.4 μm. Special care has been taken with regard to the thermal coupling of the detector. The thermal connection is made by gold layers on the fanout board and an additional spring-loaded mechanism. A warm mirror baffle system has been developed, in order to minimize the thermal background for K band observations. The camera is a focal reducer only and has no cold pupil stop.
Millisecond infrared astrophysical spectrophotometer: MIRAS
Paul M. Harvey, David Wilson
We describe an instrument under development at the University of Texas for observation of lunar occultations with complete spectral coverage from 1 - 13 μm and with limiting angular resolutions of 1 - 4 milliarcsecond over that range. The instrument will utilize three 2-D arrays that will enable spectral dispersion with a resolving power, R ~ 100, and permit pupil division to avoid blurring the Fresnel fringes of an occultation. The scientific motivation for this program is based on observations of physical properties of circumstellar disks around young, forming stars, as well as of shells around evolved stars undergoing mass loss. We also describe some examples of results with a prototype version of this instrument that has been in use at McDonald Observatory for the last 18 months.
Near-infrared camera and Fabry-Perot spectrometer: NIC-FPS
The Near-Infrared Camera and Fabry-Perot Spectrometer (NIC-FPS) will provide near-IR imaging over the wavelength range ~0.9-2.45 microns and medium resolution (R~10,000) full-field Fabry-Perot spectroscopy in the 1.5-2.4 micron range. Science observation will commence by mid 2004 on the Astrophysical Research Consortium 3.5-m telescope at the Apache Point Observatory in Sunspot, NM. NIC-FPS will allow a wide variety of extragalactic, galactic, and solar system observational programs to be conducted. NIC-FPS will support two observational modes, near-IR imaging or Fabry-Perot spectroscopy. For spectroscopy of line-emitting objects, the cryogenic Fabry-Perot etalon is inserted into the optical path to generate 3D spectral datacubes at ~30 km/s spectral resolution. For narrow to broad-band imaging, the etalon is removed from the optical path. Both modes will utilize a Rockwell Hawaii 1RG 1024 x 1024 HgCdTe detector which features low dark current, low noise and broad spectral response required for astronomical observations. The optics and detector will provide a full 4.6' × 4.6' field of view at 0.27" pixel. NIC-FPS will be mounted to the ARC telescope's Nasmyth port. NIC-FPS will significantly increase ARC's near-IR imaging and spectroscopy capabilities. We present NIC-FPS's optical design and instrument specifications.
Tohoku University focal plane array controller (TOUFPAC)
Takashi Ichikawa, Daigo Matsumoto, Kenshi Yanagisawa, et al.
TUFPAC (Tohoku University Focal Plane Array Controller) is an array control system originally designed for flexible control and efficient data acquisition of 2048 x 2048 HgCdTe (HAWAII-2) array. A personal computer operated by Linux OS controls mosaic HAWAII-2s with commercially available DSP boards installed on the PCI bus. Triggered by PC, DSP sends clock data to front-end electronics, which is isolated from the DSP board by photo-couplers. Front-end electronics supply powers, biases and clock signals to HAWAII2. Pixel data are read from four outputs of each HAWAII2 simultaneously by way of four channel preamps and ADCs. Pixel data converted to 16 bit digital data are stored in the frame memory on the DSP board. Data are processed in the memory when necessary. PC receives the frame data and stores it in the hard disk of PC in FITS format. A set of the DSP board and front-end electronics is responsible for controlling each HAWAII-2. One PC can operate eight mosaic arrays at most. TUFPAC is applicable to the control of CCDs with minor changes of front-end electronics.
Spectroscopy with adaptive optics: example and quality of GraF data
We discuss the quality of the spectro-imaging data (integral field spectroscopy) of the GraF instrument used with the ADONIS adaptive optics system at the ESO 3.6 m telescope in 1997-2001. The integral filed spectroscopy was obtained using a Fabry-Perot interferometer (FPI) in cross-dispersion with a grating spectrograph. A cube of spectro-imaging data at λ ≈ 2200 nm covers a 1.5" x 12.4" sky field sampled with 0.05" pixels; the field is recorded at 384 spectral points with the spectral resolution R ≈ 7000. The maximum field and spectral resolution are wavelength dependent, e.g. λ ≈ 1650 nm the field is 0.9" x 9" sampled with 0.035", recorded at 432 spectral points with R ≈ 10000. A spectrum of a B3III standard in the hydrogen Br-γ 2165.5 nm line and spectro-imaging of the complex central region of the eruptive star η Car in the spectral range 1668-1692 nm, including Br-11 1680.6 nm, [FeII] 1676.9 nm, FeII 1678.7 nm and FeII 1687.3 nm lines, are presented along with the discussion concentrated on the accurate calibration of the spatial point-spread function for the image deconvolution, the photometric monitoring of the FPI spectral scan channels, and on the final quality of the extracted spectra.
Fiber IFU unit for the second-generation VLT spectrograph KMOS
Daigo Tomono, Harald Weisz, Reiner Hofmann
KMOS is a cryogenic multi-object near-infrared spectrograph for the VLT. It will be equipped with about 20 deployable integral field units (IFUs) which can be positioned anywhere in the 7.2 arcmin diameter field o the VLT Nasmyth focus by a cryogenic robot. We describe IFUs using micro lens arrays and optical fibers to arrange the two-dimensional fields from the IFUs on the spectrograph entrance slit. Each micro-lens array is mounted in a spider arm which also houses the pre-optics with a cold stop. The spider arms are positioned by a cryogenic robot which is built around the image plane. For the IFUs, two solutions are considered: monolithic mirco-lens arrays with fibers attached to the back where the entrance pupil is imaged, and tapered fibers with integrated lenses which are bundled together to form a lens array. The flexibility of optical fibers relaxes boundary conditions for integration of the instrument components. On the other hand, FRD and geometric characteristics of optical fibers leads to higher AΩ accepted by the spectrograph. Conceptual design of the instrument is presented as well as advantages and disadvantages of the fiber IFUs.
Lens mounting system for cryogenic applications
Lens mounts for cryogenic service have many requirements: mitigation of thermal shock on the lens, maintenance of lens centering and spacing, control of mechanical stress on the lens from the cell, reliable connection of the lens to the cell, and applicability to a wide variety of lens materials. This paper describes in detail a lens mounting system successfully used in several cryogenic instruments.
Adjustable truss for support, optical alignment, and athermalization of a Schmidt camera
The MODS optical spectrograph uses a de-centered Maksutov-Schmidt camera with a clear aperture of ~300mm. This large camera has two widely spaced elements, the corrector and the camera mirror, and a field flattener near the focal plane. This paper describes the truss system that supports the optical elements very rigidly, uses adjustable length links to provide a deterministic method for alignment of the optical elements, and uses material combinations which result in a camera with nearly zero focus shift due to changes in temperature. A novel joint design for terminating the truss links is described that has excellent stiffness and enhances ease of assembly and alignment.
ISPI: the infrared side port imager for the CITO 4-m telescope
Ronald G. Probst, Andres Montane, Michael Warner, et al.
The new operations model for the CTIO Blanco 4-m telescope will use a small suite of fixed facility instruments for imaging and spectroscopy. The Infrared Side Port Imager, ISPI, provides the infrared imaging capability. We describe the optical, mechanical, electronic, and software components of the instrument. The optical design is a refractive camera-collimator system. The cryo-mechanical packaging integrates two LN2-cooled dewars into a compact, straightline unit to fit within space constraints at the bent Cassegrain telescope focus. A HAWAII 2 2048 x 2048 HgCdTe array is operated by an SDSU II array controller. Instrument control is implemented with ArcVIEW, a proprietary LabVIEW-based software package. First light on the telescope is planned for September 2002.
The Mauna Kea Observatories near-infrared filter set for 1-5 µm
A description of a new 1-5 micron filter set for infrared photometry is presented. This new Mauna Kea Observatories near-infrared filter set is designed to reduce background noise, improve photometric transformations from observatory to observatory, provide greater accuracy in extrapolating to zero airmass, and reduce the color dependence in the extinction coefficient in photometric reductions. Through this effort we hope to establish a single standard set of infrared filters for ground-based astronomy. A complete technical description is presented to facilitate the production of similar filters in the future.
CONICA design, performance and final laboratory tests
CONICA has been developed by a German consortium under an ESO contract, to serve together with the VLT adaptive optics system NAOS as a high resolution multimode NIR camera and spectrograph. We report on final laboratory performance tests carried out during the integration period with the adaptive optics. Apart from an outline of the capabilities of this multimode instrument such as high resolution imaging, spectroscopy, Fabry-Perot and a sophisticated internal flexure compensation, we will turn our attention to a detailed examination of the detector characteristics to fully exploit the potential of the ALADDIN array.
Characterization of the scientific grade Hawaii detector for LIRIS
Jose Acosta-Pulido, Carlos Dominguez-Tagle, Arturo Manchado
The instrument LIRIS is a near IR spectrograph to be installed at the WHT telescope. Currently it is being assembled at the Instituto de Astrofisica de Canarias. The instrument will have a Hawaii 1Kx1K array as the detector. Here we report the laboratory characterization of the scientific grade unit. We give the relevant parameters such as linearity range, gain and readout noise. These results confirm that the science grade detector will fulfil the astronomical requirements for making LIRIS a front line IR instrument. We also discuss some peculiar effects which need to be taken into account in order to guarantee a correct astronomical performance. Among these effects we consider: variation of the dark signal with integration time, cross-talk, and persistance. We also discuss the variation of the bias level with detector temperature and the need to establish an extremely stable control of the temperature.
Abu infrared imager
Nigel Sharp, Albert M. Fowler, William J. Ball
The Abu infrared imager consists of an ALADDIN 1024x1024 InSB array mounted in a cold-head cooled dewar capable of pumping down to operational temperature without cryogens, equipped with one-to-one transfer optics and an eight-position filter wheel. This simple system was operated at the South Pole on the CARA SPIREX telescope for two years, running in its second winter without trouble continuously for nine months. It was then modified slightly, mostly by inclusion of a higher quality ALADDIN II array, and used for commissioning of the Gemini South 8-meter telescope on Cerro Pachon in Chile. We discuss the lessons learned from the South Pole experiment, the changes made for operations on Gemini South, some results from both sites, and the future of this compact, reliable, and robust camera.
Wide-field infrared camera for the Palomar 200-in. telescope
John C. Wilson, Stephen S. Eikenberry, Charles P. Henderson, et al.
The availability of both large aperture telescopes and large format near-infrared (NIR) detectors are making wide-field NIR imaging a reality. We describe the Wide-field Infrared Camera (WIRC), a newly commissioned instrument that provides the Palomar 200-inch telescope with such an imaging capability. WIRC features a field-of-view (FOV) of 4.33 arcminutes on a side with its currently installed 1024-square Rockwell Hawaii-I NIR detector. A 2048-square Rockwell Hawaii-II NIR detector will be installed and commissioned later this year, in collaboration with Caltech, to give WIRC an 8.7 arcminute FOV on a side. WIRC mounts at the telescope's f/3.3 prime focus. The instrument's seeing-limited optical design, optimized for the JHK atmospheric bands, includes a 4-element refractive collimator, two 7-position filter wheels that straddle a Lyot stop, and a 5-element refractive f/3 camera. Typical seeing-limited point spread functions are slightly oversampled with a 0.25 arcsec per pixel plate scale at the detector. The entire optical train is contained within a cryogenic dewar with a 2.5 day hold-time. Entrance hatches at the top of the dewar allow access to the detector without disruption of the optics and optical alignment. The optical, mechanical, cryogenic, and electronic design of the instrument are described, a commissioning science image and performance analyses are presented.
SIRIUS: a near-infrared simultaneous three-band camera
Takahiro Nagayama, Chie Nagashima, Yasushi Nakajima, et al.
We developed a near infrared simultaneous three-band (J, H and Ks) camera, SIRIUS. The design of SIRIUS is optimized to deep, large area surveys in the three IR bands. SIRIUS is equipped with three 1024 x 1024 HgCdTe (HAWAII) arrays, providing simultaneous three-band images. SIRIUS has obtained its first light on the UH 2.2 m telescope in August 2000. SIRIUS is now mounted on the IRSF 1.4 m telescope in Sutherland and is dedicated to deep survey in the southern sky from November 2000. On this telescope, SIRIUS provides 7'.8 x 7'.8 field of view with a pixel scale of 0".45 in all bands. The typical limiting magnitudes are J = 19.2 mag, H = 18.6 mag, Ks = 17.3 mag (15 min. integration, S/N = 10 σ). The effective exposure time (30 sec exposure for each frame) in an hour is about 37 minutes (60%) for each band. Both the instrument and the 1.4 m telescope are in operation.
SALTICAM, $0.5M-acquisition camera: every big telescope should have one
Darragh O'Donoghue, Etienne Bauermeister, David B. Carter, et al.
The Southern African Large Telescope (SALT) is a 10-m class telescope presently under construction at Sutherland in South Africa. It is designed along the lines of the Hobby-Eberly Telescope (HET) at McDonald Observatory in West Texas. SALTICAM will be the Acquisition Camera and simple Science Imager (ACSI) for this telescope. It will also function as the Verification Instrument (VI) to check the performance of the telescope during commissioning. In VI mode, SALTICAM will comprise a filter unit, shutter and cryostat with a 2x1 mosaic of 2k x 4k x 15 micron pixel CCDs. It will be mounted at the f/4.2 corrected prime focus of the telescope. In ACSI mode it will be fed by a folding flat located close to the exit pupil of the telescope. ACSI mode will have the same functional components as VI mode but it will in addition be garnished with focal conversion lenses to re-image the corrected prime focal plane at f/2. The lenses will be made from UV transmitting crystals as the wavelength range for which the instrument is designed will span 320 to 950 nm. In addition to acting as Verification Instrument and Acquisition Camera, SALTICAM will perform simple science imaging in support of other instruments, but will also have a high time resolution capability which is not widely available on large telescopes. This paper will describe the design of the instrument, emphasizing features of particular interest.
Optical design for a thermal infrared wide-field camera for the Large Binocular Telescope
Eberhard Dietzsch, Bringfried Stecklum, Werner Pfau, et al.
The Large Binocular Telescope (LBT) will provide unique observing capabilities in terms of angular resolution and field size. The Fizeau combination of the beams from the two telescope apertures produces an intermediate image which shall be imaged onto a detector array. For this purpose, we designed an optical instrument, the thermal infrared wide-field camera described below. During its design, special care was taken to properly treat the synthetic aperture. The result is a catadioptric optical system with interchangable magnifications matched to the spectral regions around 10 and 20 μm. We present the optical design along with the image analysis.
CFHT MegaCam control system: new solutions based on PLCs, WorldFIP fieldbus and Java softwares
Jean Yves Rousse, Olivier Boulade, Xavier Charlot, et al.
MegaCam is a wide-field imaging camera built for the prime focus of the 3.6m Canada-France-Hawaii Telescope. This large detector has required new approaches from the hardware up to the instrument control system software. Safe control of the three sub-systems of the instrument (cryogenics, filters and shutter), measurement of the exposure time with an accuracy of 0.1%, identification of the filters and management of the internal calibration source are the major challenges that are taken up by the control system. Another challenge is to insure all these functionalities with the minimum space available on the telescope structure for the electrical hardware and a minimum number of cables to keep the highest reliability. All these requirements have been met with a control system which different elements are linked by a WorldFip fieldbus on optical fiber. The diagnosis and remote user support will be insured with an Engineering Control System station based on software developed on Internet JAVA technologies (applets, servlets) and connected on the fieldbus.
A tunable filter for the TNG
Many astronomical researches make use of narrow-band observations to isolate specific spectral features. We present a project to implement an imaging tunable interference filter, representing an observational facility that can greatly expand the capabilities of the instrumentation currently mounted at TNG.
CFHT MegaCam filter, shutter and roll pitch mechanisms
Stephan Aune, Olivier Boulade, Xavier Charlot, et al.
MegaCam is an imaging CCD camera with a 1 square degree field of view for the new MegaPrime prime focus of the 3.6 meter Canada-France-Hawaii Telescope. This CCD camera is fixed on an aluminum structure, called Camembert for its shape, housing a shutter, a filter system and a roll pitch system to tune the CCD mosaic plane. The shutter is made with 1 meter diameter honeycomb half disks that rotates to covers or exposes the CCD mosaic. On this shutter a calibration source is fixed to monitor the CCD and its electronics. The filter system is made of a jukebox with a capacity of eight 30 cm square filters and of a loading arm to place them under the field of view. The instrument was delivered to the CFHT observatory on June 10, 2002 and first light is scheduled in October 2002.
The CFHT MegaCam 40 CCDs camera: cryogenic design and CCD integration
Stephan Aune, Olivier Boulade, Xavier Charlot, et al.
MegaCam is an imaging camera with a 1 square degree field of view for the new prime focus of the 3.6 meter Canada-France-Hawaii Telescope. In building the MegaCam mosaic we encountered unprecedented challenges from both the large size of each CCD device (2K x 4.5K with 13.5 micron square pixels each) and the large size of the mosaic in which 40 devices have been assembled in a nearly 4-buttable edge manner on a cold plate. The CCD mosaic flatness of ± 16 μm has been optically checked at its nominal functioning temperature. The CCD mosaic is cooled at 153 K with a cryogenic unit; a close cycle pulsed tube with a power of 90 W at 140 K. A cold capacity, allows a slow warm-up during cooling shutdowns and a thermal dispatching leads to a temperature uniformity better than 3 K on the whole mosaic. The camera cryostat is designed in order to have easy access to the CCDs. The vacuum needed to avoid CCD contamination, leaded us to the use of low out-gassing materials in the cryostat. The instrument was delivered to the observatory on June 10, 2002 and first light is scheduled in October 2002.
NEWFIRM: the widefield infrared imager for NOAO 4-m telescopes
Roy Gene Autry, Ronald G. Probst, Barry Michael Starr, et al.
Wide field-of-view, high-resolution near-infrared cameras on 4-m class telescopes have been identified by the astronomical community as critical instrumentation needs in the era of 8-m and larger telescopes. Acting as survey instruments, they will provide the input source discoveries for large-telescope follow-up observations. The NOAO Extremely Wide Field Infrared Mosaic (NEWFIRM) imaging instrument will serve this need within the US system of facilities. NEWFIRM is being designed for the National Optical Astronomy Observatory (NOAO) 4-m telescopes (Mayall at KPNO and Blanco at CTIO). NEWFIRM covers a 28 x 28 arcmin field of view over the 1-2.4 μm wavelength range with a 4k x 4k pixel detector mosaic assembled from 2k x 2k modules. Pixel scale is 0.4 arcsec/pixel. Data pipelining and archiving are integral elements of the instrument system. We present the science drivers for NEWFIRM, and describe its optical, mechanical, electronic, and software components. By the time this paper is presented, NEWFIRM will be in the preliminary design stage, with first light expected on the Mayall telescope in 2005.
Six degree-of-freedom positioner for optical components
The Six Degree-of-Freedom (6DOF) positioner was developed to position the four off-axis conic mirrors in Altair (Gemini** North's facility adaptive optics system). This positioner takes a unique approach to 6DOF positioning by combining two 3DOF parallel mechanisms in series to create a hybrid mechanism. The mechanism design provides a number of benefits including small size, simple adjustment, position locking, relatively simple kinematics and repeatable removal and replacement of optical components. The 6DOF positioner is capable of positioning optics at the micron level in translation and at the arcsecond level in rotation. It also maintains the position of the optics to a few microns with changing gravity vector. The position of an attached optical component can be adjusted using a computer program to provide precision adjustment about an arbitrary coordinate system. However, the arrangement of the adjustments are such that any desired motion can be made with a single actuator or with a sensible combination of actuators. This is unlike other 6DOF positioning solutions like a Stewart Platform in which all 6DOF are completely coupled making it impossible to move the platform in any desired direction without moving all six actuators. This paper will present the design of the positioner, a kinematic analysis of the mechanism and a discussion about the effectiveness of the positioner in the optical alignment of Altair.
Blue and red channels of LBC: a status report on the optics and the mechanics
The Large Binocular Camera (LBC) is a double prime focus station to be mounted on the Large Binocular Telescope (LBT). The two channels, called Blue and Red, are optimized for the UB and VRIZ bands respectively and are characterized by two optical correctors with very fast focal ratio (F/1.45) and challenging optical and mechanical specifications. We present here a review of the optical and mechanical design of both the optical correctors and report on the current status of the manufacturing and integration.
ASTROCAM: an Offner re-imaging 1024 x 1024 InSb camera for near-infrared astrometry on the USNO 1.55 m telescope
Jacqueline Fischer, Frederick J. Vrba, Douglas W. Toomey, et al.
In order to extend the US Naval Observatory (USNO) small-angle astrometric capabilities to near infrared wavelengths we have designed and manufactured a 1024 x 1024 InSb re-imaging infrared camera equipped with an array selected from the InSb ALADDIN (Advanced Large Area Detector Development in InSb) development program and broadband and narrowband 0.8 - 3.8 μm filters. Since the USNO 1.55-m telescope is optimized for observations at visible wavelengths with an oversized secondary mirror and sky baffles, the straylight rejection capabilities of the ASTROCAM Lyot stop and baffles are of critical importance for its sensitivity and flat- fielding capabilities. An Offner relay was chosen for the heart of the system and was manufactured from the same melt of aluminum alloy to ensure homologous contraction from room temperature to 77 K. A blackened cone was installed behind the undersized hole (the Lyot stop) in the Offner secondary. With low distortion, a well-sampled point spread function, and a large field of view, the system is well suited for astrometry. It is telecentric, so any defocus will not result in a change of image scale. The DSP-based electronics allow readout of the entire array with double-correlated sampling in 0.19 seconds, but shorter readout is possible with single sampling or by reading out only small numbers of subarrays. In this paper we report on the optical, mechanical, and electronic design of the system and present images and results on the sensitivity and astrometric stability obtained with the system, now operating routinely at the 1.55-m telescope with a science-grade ALADDIN array.
Micromachined tunable Fabry-Perot filters for infrared astronomy
D. Brent Mott, Richard B. Barclay, Alexander Bier, et al.
Micromachined Fabry-Perot tunable filters with a large clear aperture (12.5 to 40 mm) are being developed as an optical component for wide-field imaging spectroscopy. This program applies silicon micromachining fabrication techniques to miniaturize Fabry-Perot filters for astronomical science instruments. The filter assembly consists of two reflector plates that form a tunable Fabry-Perot etalon. One plate is fixed and the second plate is free to move along the optical axis on silicon springs. The moving plate is actuated electrostatically by capacitance pads on the stationary and moving plates. To reduce mass, both reflectors are fabricated by applying optical coatings to a thin freestanding silicon nitride film held flat in drumhead tension. In this paper, we discuss the etalon design, electromechanical modeling, fabrication, and initial results. In the current design, the transmission aperture is 11.0 mm in diameter, the moving plate is 26.3 mm in diameter, and the stationary plate is 32.6 mm in diameter. The plates and springs are nominally 350 μm thick, the electrical and mechanical spacing between plates is 18 μm, and the uncoated optical spacing is 15 μm.
AEOS burst camera: project description
Mark A. Skinner, Carl W. Akerlof, Timothy McKay, et al.
The AEOS Burst Camera (ABC) has been funded for development and construction by the National Science Foundation and the Air Force Office of Scientific Research. The ABC will provide rapid, deep observations of gamma-ray burst (GRB) optical counterparts. The camera is expected to be installed on the 3.67 meter AEOS telescope, at the Air Force Maui Optical and Supercomputing (AMOS) site in mid-2002, with operations to commence shortly thereafter. We expect to conduct six observations of GRB optical counterparts per year. We describe the design of the camera, and the planned mode of rapid GRB counterpart observation to be conducted at the AMOS facility. Results of the initial operations of the camera will also be reported.
Dual infrared camera for near- and mid-infrared observations
We present the dual IR camera CID for the 2.12 m telescope of the Observatorio Astronomico Nacional de Mexico, IA-UNAM. The system consists of two separate cameras/spectrographs that operate in different regions of the IR spectrum. In the near IR, CID comprises a direct imaging camera with wide band filters, a CVF, and a low resolution spectrograph employing an InSb 256 x 256 detector. In the mid IR, CID uses a BIB 128 x 128 detector for direct imaging in 10 and 20 microns. Optics and mechanics of CID were developed at IR-Labs (Tucson). The electronics was developed by R. Leach (S. Diego). General design, construction of auxiliary optics (oscillating secondary mirror), necessary modifications and optimization of the electronics, and acquisition software were carried out at OAN/ UNAM. The compact design of the instruments allow them to share a single dewar and the cryogenics system.
Monsoon: image acquisition system or "pixel server"
The MONSOON Image Acquisition System has been designed to meet the need for scalable, multichannel, high-speed image acquisition required for the next-generation optical and infared detectors and mosaic projects currently under development at NOAO as described in other papers at this proceeding such as ORION, NEWFIRM, QUOTA, ODI and LSST. These new systems with their large scale (64 to 2000 channels) and high performance (up to 1Gbyte/s) raise new challenges in terms of communication bandwidth, data storage and data processing requirements which are not adequately met by existing astronomical controllers. In order to meet this demand, new techniques for not only a new detector controller, but rather a new image acquisition architecture, have been defined. These extremely large scale imaging systems also raise less obvious concerns in previously neglected areas of controller design such as physical size and form factor issues, power dissipation and cooling near the telescope, system assembly/test/ integration time, reliability, and total cost of ownership. At NOAO we have taken efforts to look outside of the astronomical community for solutions found in other disciplines to similar classes of problems. A large number of the challenges raised by these system needs are already successfully being faced in other areas such as telecommunications, instrumentation and aerospace. Efforts have also been made to use true commercial off the shelf (COTS) system elements, and find truly technology independent solutions for a number of system design issues whenever possible. The Monsoon effort is a full-disclosure development effort by NOAO in collaboration with the CARA ASTEROID project for the benefit of the astronomical community.
Optically athermalized construction optical design for the IMACS short camera
Harland W. Epps, Brian M. Sutin
The optical performance of a large, optically fast, all-refracting spectrograph camera is extremely sensitive to potential temperature changes which might occur during an extended signle observation, over the duration of an observing run, and/or on seasonal time scales. A small temprature change, even at the level of a few degrees C, will lead to changs in the rerfractive indices of the glasses and the coupling medium, changes in the lens-element geometries and in the dimensions of the lens cell. These effects combine in a design-specific manner to cause potential changes of focus and magnification within the camera as well as inherent loss of image quality. We have used an optical design technique originally developed for the Smithsonian Astrophysical Observatory's BINOSPEC instrument in order to produce a construction optical design for the Carnegie IMACS Short camera. This design combines the above-mentioned temperature-dependent parameter variations in such a way that their net effect upon focus and magnification is passively reduced to negligible residuals, without the use of high-expansion plastics, "negative-c.t.e." mechanisms or active control within the lens cell. Simultaneously, the design is optimized for best inherent image quality at any temperature within the designated operating range. The optically-athermalized IMACS Short camera is under construction. We present its quantitative optical design together with our assessment of its expected performance over a (T = -4.0 to +20.0) C temperature range.
Pupil-segmented photometry for lunar occultation observation
Occultation is potentially a powerful tool for high-resolution astronomy. It can reach about a few milli-arcsec (mas) by lunar occultation observation and 0.1 mas by that of main-belt asteroids. Photon noise limits the resolution. If we use large telescope in order to increase the number of photons received by a telescope, the fringe pattern that is projected on the earth is averaged over the pupil and the visibility will decrease. I propose to use pupil-segmented method and its performance for lunar occultation. The optimum subaperture size is 2-4 m for lunar occultation. This method is effective for large (> 8-10m) telescope. We can resolve in 6 mas for 16 mag star in > 3 σ noise level using 8 m telescope.
REM-IR camera: high-quality near-infrared imaging with a small robotic telescope
Fabrizio Vitali, Filippo Maria Zerbi, Guido Chincarini, et al.
We present the near infrared camera REM-IR that will operate aboard the REM telescope, intended as a fully automated instrument to follow-up Gamma Ray Burst, triggered mainly by satellites, such as HETE II, INTEGRAL, AGILE and SWIFT. REM-IR will perform high efficiency imaging of the prompt infrared afterglow of GRB and, together with the optical spectrograph ROSS, will cover simultaneously a wide wavelength range, allowing a better understanding of the intriguing scientific case of GRB. Due to the scientific and technological requirements of the REM project, some innovative solutions has been adopted in REM-IR.
The project INCA: engineering of NIR (1-5 µm) cameras for ground- and space-based astronomical applications
Filippo Maria Zerbi, Florio Dalla Vedova, Alessandro Batocchio, et al.
We present a status report of the R&D project INCA, aimed to create in a selected group of Italian SME the expertise to build high quality Infrared instrumentation for Astronomy. The INCA consortium is currently building a fully functional test NIR-camera (1-5 μm) exploring any sort of innovation in the field of optics (new materials, aspheric surfaces), mechanics/cryogenics (new concept in lens holding, light-weighted structures, cryo-pumps) and electronics (new chip controllers). The camera will be installed for testing at one of the major telescope facility available to the Italian community and its performances in true astronomical applications evaluated.
Two-channel robotic CCD camera
Claus A. Goessl, Wolfgang Mitsch, Werner Altmann, et al.
We present the design of a compact two-channel CCD-camera for the 0.8 m Cassegrain telescope operated at the Wendelstein Observatory. To achieve a high efficiency this camera is equipped with two channels, operating in the wavelength range of 400 - 540 nm and 570 - 900 nm, respectively. Each channel is provided with a filter slider for three positions, an independent photometric shutter, and a 2k x 2k CCD (80% peak efficiency). The camera can simultaneously record a red and a blue image of its 10.7' x 10.7' field of view. In addition it has an offset guider and supports robotic operation: Active cooling provides the operating temperature of 160 K avoiding the use of liquid nitrogen. Both CCDs share a single cryostat and can be aligned during operation. The complete vacuum control including pumping and cryopump cleaning can be operated remotely.
Design of cryomechanisms for infrared astronomy
The Laboratoire d'Astrophysique Experimentale (LAE) at the Universite de Montreal has designed and built several near-infrared cameras/spectrometers in the last decade for the Observatoire du Mont-Mégantic (OMM), the Canada-France-Hawaii Telescope (CFHT) and the Herzberg Institute of Astrophysics (HIA). These instruments have required innovative solutions for cryogenic electro-mechanical controls. This paper presents cryogenic motors, bearings, gears, epoxies and positioning/sensing devices at the heart of these cryo-mechanisms. In particular, the paper will focus on a new ball plunger with integrated Hall effect sensor, which can be used both as a mechanical detent and analog position encoder.
Hobby-Eberly Telescope: LRS-J HAWAII-1 detector electronics
The first second-generation instrument for the Hobby-Eberly telescope is a novel J band camera (LRS-J) which mates to the existing low resolution spectrograph (LRS). This camera uses the existing LRS longslit and mutltiobject units as well as the LRS five element collimator but uses its own J optimized volume holographic grisms, f/1 cryogenically cooled camera, and readout electronics built around a Rockwell HAWAII-1 array. We minimized the development time of the controller by reusing as much of the existing framework as possible. The modular design of the existing LRS CCD controller allows us to modify only the clock-driver and penthouse (pre-amplifier) modules. Furthermore, we were able to use existing multilayer circuit boards already fabricated for these two modules. Thus, the LRS-J controller required only the substitution of components on two modules and the design of a new header (dewar) board to fit the HAWAII-1 socket. With these modifications, based on its perfomance with CCDs, we predict a noise and crosstalk performance at the most competitive level.
Design and fabrication of diamond-machined aspheric mirrors for ground-based near-IR astronomy
Raymond G. Ohl IV, Werner Preuss, Alex Sohn, et al.
Challenges in fabrication and testing have historically limited the choice of surfaces available for the design of reflective optical instruments. Spherical and conic mirrors are common, but, for future science instruments, more degrees of freedom will be necessary to meet performance and packaging requirements. These instruments will be composed of surfaces of revolution located far off-axis with large spherical departure, and some designs will even require asymmetric surface profiles. We describe the design and diamond machining of seven aluminum mirrors: three rotationally symmetric, off-axis conic sections, one off-axis biconic, and three flat mirror designs. These mirrors are for the Infrared Multi-Object Spectrometer instrument, a facility instrument for the Kitt Peak National Observatory’s Mayall Telescope (3.8 m) and a pathfinder for the future Next Generation Space Telescope multi-object spectrograph. The symmetric mirrors include convex and concave prolate and oblate ellipsoids, and range in aperture from 92 x 77 mm to 284 x 264 mm and in f-number from 0.9 to 2.4. The biconic mirror is concave and has a 94 x 76 mm aperture, (formula available in paper) and is decentered by -2 mm in x and 227 mm in y. The mirrors have an aspect ratio of approximately 6:1. The fabrication tolerances for surface error are < 63.3 nm RMS figure error and < 10 nm RMS microroughness. The mirrors are attached to the instrument bench using semi-kinematic, integral flexure mounts and optomechanically aligned to the instrument coordinate system using fiducial marks and datum surfaces. We also describe in-process profilometry and optical testing.
Optical testing of diamond-machined aspheric mirrors for ground-based, near-IR astronomy
John Chambers, Ronald G. Mink, Raymond G. Ohl IV, et al.
The Infrared Multi-Object Spectrometer (IRMOS) is a facility-class instrument for the Kitt Peak National Observatory 4 and 2.l meter telescopes. IRMOS is a near-IR (0.8-2.5 μm) spectrometer and operates at ~80 K. The 6061-T651 aluminum bench and mirrors constitute an athermal design. The instrument produces simultaneous spectra at low- to mid-resolving power (R = λ/Δλ = 300-3000) of ~100 objects in its 2.8×2.0 arcmin field. We describe ambient and cryogenic optical testing of the IRMOS mirrors across a broad range in spatial frequency (figure error, mid-frequency error, and microroughness). The mirrors include three rotationally symmetric, off-axis conic sections, one off-axis biconic, and several flat fold mirrors. The symmetric mirrors include convex and concave prolate and oblate ellipsoids. They range in aperture from 94×86 mm to 286×269 mm and in f-number from 0.9 to 2.4. The biconic mirror is concave and has a 94×76 mm aperture, Rx=377 mm, kx=0.0778, Ry=407 mm, and ky=0.1265 and is decentered by -2 mm in X and 227 mm in Y. All of the mirrors have an aspect ratio of approximately 6:1. The surface error fabrication tolerances are < 10 nm RMS microroughness, best effort for mid-frequency error, and < 63.3 nm RMS figure error. Ambient temperature (~293 K) testing is performed for each of the three surface error regimes, and figure testing is also performed at ~80 K. Operation of the ADE PhaseShift MicroXAM white light interferometer (micro-roughness) and the Bauer Model 200 profilometer (mid-frequency error) is described. Both the sag and conic values of the aspheric mirrors make these tests challenging. Figure testing is performed using a Zygo GPI interferometer, custom computer generated holograms (CGH), and optomechanical alignment fiducials. Cryogenic CGH null testing is discussed in detail. We discuss complications such as the change in prescription with temperature and thermal gradients. Correction for the effect of the dewar window is also covered. We discuss the error budget for the optical test and alignment procedure. Data reduction is accomplished using commercial optical design and data analysis software packages. Results from CGH testing at cryogenic temperatures are encouraging thus far.
Imaging performance and modeling of the infrared multi-object spectrometer focal reducer
The Infrared Multi-Object Spectrometer (IRMOS) is a facility instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 μm) spectrometer with low- to mid-resolving power (R = 300 - 3000). The IRMOS spectrometer produces simultaneous spectra of ~100 objects in its 2.8 x 2.0 arcmin field of view using a commercial MEMS multi-mirror array device (MMA) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the MMA field stop, and the spectrograph images the MMA onto the detector. We describe the breadboard subsystem alignment method and imaging performance of the focal reducer. This testing provides verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Interferometric measurements of subsystem wavefront error serve to verify alignment and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing is then performed for the central field point. A mercury-argon pencil lamp provides the spectral line at 546.1 nm, and a CCD camera is the detector. We use the Optical Surface Analysis Code to predict the point-spread function and its effect on instrument slit transmission, and our breadboard test results validate this prediction. Our results show that scattered light from the subsystem and encircled energy is slightly worse than expected. Finally, we perform component level image testing of the MMA, and our results show that scattered light from the MMA is of the same magnitude as that of the focal reducer.
The AVES adaptive optics spectrograph for the VLT: status report
Roberto Pallavicini, Bernard Delabre, Luca Pasquini, et al.
We report on the status of AVES, the Adaptive-optics Visual Echelle Spectrograph proposed for the secondary port of the Nasmyth Adaptive Optics System (NAOS) recently installed at the VLT. AVES is an intermediate resolution (R ≈ 16,000) high-efficiency fixed- format echelle spectrograph which operates in the spectral band 500 - 1,000 nm. In addition to a high intrinsic efficiency, comparable to that of ESI at Keck II, it takes advantage of the adaptive optics correction provided by NAOS to reduce the sky and detector contribution in background-limited observations of weak sources, thus allowing a further magnitude gain with respect to comparable non-adaptive optics spectrographs. Simulations show that the instrument will be capable of reaching a magnitude V = 22.5 at S/N > 10 in two hours, two magnitudes weaker than GIRAFFE at the same resolution and 3 magnitudes weaker than the higher resolution UVES spectrograph. Imaging and coronographic functions have also been implemented in the design. We present the results of the final design study and we dicuss the technical and operational issues related to its implementation at the VLT as a visitor instrument. We also discuss the possibility of using a scaled-up non-adaptive optics version of the same design as an element of a double- or triple-arm intermediate-resolution spectrograph for the VLT. Such an option looks attractive in the context of a high-efficiency large-bandwidth (320 - 1,500 nm) spectrograph ("fast-shooter") being considered by ESO as a 2nd-generation VLT instrument.
Design of the IMACS 8Kx8K dewar and detector system
Bruce C. Bigelow, Gerard Anthony Luppino, Gregory S. Burley, et al.
The Inamori-Magellan Areal Camera and Spectrograph (IMACS) features a 8K x 8K, 6.7 Megapixel detector system, which is mounted in a cryogenic vacuum vessel with a combination of features that are unique among the current generation of astronomical multi-detector array systems. Closed-cycle coolers, commercial stages for flexure compensation, flexure control detectors, array focus control, composite thermal isolation truss and other features are described.
REM telescope: a robotic facility to monitor the prompt afterglow of gamma ray bursts
Filippo Maria Zerbi, Guido Chincarini, Gabriele Ghisellini, et al.
Observations of the prompt afterglow of Gamma Ray Burst events are unanimously considered of paramount importance for GRB science and cosmology. Such observations at NIR wavelengths are even more promising allowing one to monitor high-z Ly-α absorbed bursts as well as events occurring in dusty star-forming regions. In these pages we present REM (Rapid Eye Mount), a fully robotized fast slewing telescope equipped with a high throughput NIR (Z, J, H, K) camera dedicated to detecting the prompt IR afterglow. REM can discover objects at extremely high redshift and trigger large telescopes to observe them. The REM telescope will simultaneously feed ROSS (REM Optical Slitless spectrograph) via a dichroic. ROSS will intensively monitor the prompt optical continuum of GRB afterglows. The synergy between the REM-IR camera and the Ross spectrograph makes REM a powerful observing tool for any kind of fast transient phenomena. Beside its ambitious scientific goals, REM is also technically challenging since it represent the first attempt to locate a NIR camera on a small telescope providing, with ROSS, unprecedented simultaneous wavelength coverage on a telescope of this size.
Optical Detectors and Cameras
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Highlights of Scientific Detectors Workshop 2002: the workshop of (in)famous characters in the detector community
This paper provides an overview of the “Scientific Detectors Workshop 2002”, a 5 day meeting held on the Big Island of Hawaii in June 2002. The purpose of this workshop, which is held every 3 years, is to bring together the leading scientists and engineers working in the field of optical and infrared detectors. The 125 participants came from 14 countries on 6 continents and included representation from every major detector designer/manufacturer and 27 astronomical observatories. This paper is a synthesis of the information presented at the workshop. In order to provide context, we begin with an introduction to the use of optical/IR detectors in astronomy and the basic steps in light detection. We then present the major developments in optical and infrared detectors. We conclude with information about the 2002 workshop format and give advance notice of the next workshop, scheduled for 2005.
Megapixel and larger readouts and FPAs for visible and infrared astronomy
David J. Gulbransen, Peter J. Love, Mark P. Murray, et al.
The desire for larger and larger format arrays for astronomical observatories -- both ground and space based -- has fueled the development of detector, readout, and hybrid Focal Plane Array (FPA) technology that has paved the way for later development of tactical and strategic arrays for military applications. Since 1994, Raytheon has produced megapixel readouts and FPAs for Infrared Astronomy. In 1999 Raytheon demonstrated a revolutionary approach to photolithography called Reticle Image Composition Lithography (RICL) that opened the door to very large format FPAs in state of the art sub-micron CMOS processes. The first readout processed using the patented RICL technique was a 4.2 megapixel readout for astronomy. We present the design and performance of several 4.2 megapixel (2048 x 2048) readout arrays for visible and infrared astronomy applications. The first of these arrays are fabricated in a workhorse 2 μm CMOS process that is optimized for low temperature operation (down to as low as 6 Kelvin). Most recently Raytheon has developed a scaleable 2,048 x 2,048 high density array for several ground based astronomical applications. This array can be manufactured in any m x n multiple of a basic 1024 (V) x 512 (H) pixel array core. The primary design is a 2 x 4 array to yield a 2,048 x 2,048 format array. This same design can be extended to at least a 4,096 x 4,096 format array -- an incredible 16.7 megapixel array! These readouts are compatible with a wide range of detector types including InSb, HgCdTe, and Si detectors. The use of hybrid technology -- even for the visible wavebands -- allows 100% optical fill factors to be achieved. The design and performance of these megapixel class detectors, readouts, and FPAs will be presented.
The future of imaging photon counting detectors for ground-based astronomy
Silicon Charge-Coupled Devices (CCDs) are the ubiquitous detector of choice for most ground based optical cameras given their high QE, low readout noise, good spatial resolution and large array size. However, they are integrating detectors, and as such have a limited temporal resolution determined by the readout frame rate. Imaging photon counters, on the other hand, can determine the location and arrival time of an individual detected photon which lends itself to studies of the intrinsic variability of astronomical sources. This topic is of fundamental importance, especially for the case of compact objects in stellar binary systems, stellar flares, and accretion disk phenomena. Most of these timing observations are currently performed by satellite-born X-ray instruments, but similar data can also be obtained from ground-based observatories at visible wavelengths using photon counting detectors. In this paper we review the recent and future improvements in the performance of imaging, photon counters, especially their optical QE, array size, spatial and temporal resolution and dark counting rates. We will compare them to conventional CCD devices and discuss the observational applications for which either or both can excel. We find that for certain applications (such as high time resolution observations, faint spectra and wavefront sensors for adaptive optics) imaging photon counting detectors can provide observations of superior signal-to-noise to CCD's.
12x10 pixel superconducting tunnel junction array based spectro-photometer of optical astronomy
Superconducting Tunnel Junctions (STJs) have been extensively investigated as photon detectors covering the range from near-infrared to X-ray energies. A 6x6 array of Tantalum junctions has already been used in an optical spectro-photometer. With this camera, the European Space Agency has performed multiple astronomical observations of optical sources using the William Herschel 4.2m telescope at La Palma. Following the success of this program, we are now developing a second generation camera. The goals of this program are to increase the field of view of the instrument from 4"x4" to 11"x9", to optimize IR rejection filters, possibly extending the 'red' response to ~1μm and to increase the electronics readout speed. For these purposes, we are developing a new Superconducting Tunnel Junction Array consisting of 10x12 Tantalum/Aluminium devices as well as an improved readout system. In this paper, we review the instrument's architecture and describe the performance of the new detector.
LBC: the prime focus optical imagers at the LBT telescope
The Large Binocular Camera (LBC) is the double optical imager that will be installed at the prime foci of the Large Binocular Telescope (2x8.4 m). Four Italian observatories are cooperating in this project: Rome (CCD Camera), Arcetri-Padua (Optical Corrector) and Trieste (Software). LBC is composed by two separated large field (27 arcmin FOV) cameras, one optimized for the UBV bands and the second for the VRIZ bands. An optical corrector balances the aberrations induced by the fast (F#=1.14) parabolic primary mirror of LBT, assuring that the 80% of the PSF encircled energy falls inside one pixel for more of the 90% of the field. Each corrector uses six lenses with the first having a diameter of 80cm and the third with an aspherical surface. Two filter wheels allow the use of 8 filters. The two channels have similar optical designs satisfying the same requirements, but differ in the lens glasses: fused silica for the "blue" arm and BK7 for the "red" one. The two focal plane cameras use an array of four 4290 chips (4.5x2 K) provided by Marconi optimized for the maximum quantum efficiency (85%) in each channel. The sampling is 0.23 arcseconds/pixel. The arrays are cooled by LN2 cryostats assuring 24 hours of operation. Here we present a description of the project and its current status including a report about the Blue camera and its laboratory tests. This instrument is planned to be the first light instrument of LBT.
A Novel Double Imaging Camera (ANDICAM)
Darren L. DePoy, Bruce Atwood, Stanley Ralph Belville, et al.
We describe an instrument that is capable of taking simultaneous images at one optical (UBVRI) and one near-infrared (JHK) wavelength. The instrument uses relatively simple optics and a dichroic to image the same field on to an optical CCD and an HgCdTe array. The mechanical and thermal design is similar to previous instruments built by our group and the array controllers are based on the same architecture. The instrument has been in use for the past four years on the CTIO/Yale 1m telescope in Chile and has an excellent operational/reliability record. A number of notable science results have been obtained with the instrument; especially interesting are several photometric monitoring projects that have been possible, since the instrument is available every night on the telescope.
IR Detectors and Cameras
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Review of the state of infrared detectors in retrospect of the June 2002 workshop on Scientific Detectors for astronomy
Only two months ago, in June 2002, a workshop on scientific detectors for astronomy was held in Waimea, where for the first time both experts on optical CCD's and infrared detectors working at the cutting edge of focal plane technology gathered. An overview of new developments in optical detectors such as CCD's and CMOS devices will be given elsewhere in these proceedings. This paper will focus on infrared detector developments carried out at the European Southern Observatory ESO and will also include selected highlights of infrared focal plane technology as presented at the Waimea workshop. Three main detector developments for ground based astronomers are currently pushing infrared focal plane technology. In the near infrared from 1 to 5 μm two technologies, both aiming for buttable 2K x 2K mosaics, will be reviewed, namely InSb and HgCdTe grown by LPE or MBE on Al2O3, Si or CdZnTe substrates. Blocked impurity band Si:As arrays cover the mid infrared spectral range from 8 to 28 μm. Since the video signal of infrared arrays, contrary to CCD's, is DC coupled, long exposures with IR arrays are extremely susceptible to drifts and low frequency noise pick-up down to the mHz regime. New techniques to reduce thermal drifts and suppress low frequency nosie with on-chip reference pixels will be discussed. The need for the development of small format low noise sensors for adaptive optics and interferometry will be pointed out.
Orion: the largest infrared hybrid focal plane in production
Albert M. Fowler, Michael Merrill, William J. Ball, et al.
Orion is a program to develop a 2048x2048 infrared focal plane using InSb PV detectors. It is the natural follow-on to the successful Aladdin 1024x1024 program, which was the largest IR focal plane of the 90's. Although the pixels are somewhat smaller than Aladdin, the overall focal plane is over 50mm in size and for the present is the largest IR focal plane of the 21st century. The work is being done by Raytheon Infrared Operations (RIO but better known as SBRC) by many of the same people who created the Aladdin focal plane. The design is very similar to the successful Aladdin design with the addition of reference pixels to lower noise and drift effects in long integrations. So far we have made five focal plane modules with hybridized InSb detectors. In this paper we will discuss the unique design features of this device as well as present test data taken from these devices.
First diffraction-limited images at VLT with NAOS and CONICA
In November 2001, the VLT has been equipped for the first time with an adaptive optics system, NAOS. NAOS has been designed to provide good image quality over a wide range of conditions, allowing thus a large variety of astrophysical programs, from Solar System to extragalactic studies. NAOS feeds a camera CONICA which provides imaging, coronagraphic, spectroscopic and polarimetric capabilities between 1 and 5 microns. NAOS and CONICA (hereafter NACO) have been commissioned over the past months. We present in this paper the first images recorded by NACO during the commissioning period, illustrating the capabilities of this new instrument.
IR Spectrographs I/Cameras I
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NAOS-CONICA first on-sky results in a variety of observing modes
The Adaptive Optics NIR Instrument NAOS-CONICA has been commissioned at the VLT (UT4) between November 2001 and March 2002. After summarizing the observational capabilities of this multimode instrument in combination with the powerful AO-system, we will present first on sky results of the instrumental performance for several non-direct imaging modes: High spatial resolution slit-spectroscopy in the optical and thermal NIR region has been tested. For compact sources below 2 arcsec extension, Wollaston prism polarimetry is used. For larger objects the linear polarization pattern can be analyzed by wire grids down to the diffraction limit. Coronographic masks are applied to optimize imaging and polarimetric capabilities. The cryogenic Fabry-Perot Interferometer in combination with an 8m-telescope AO-system is shown to be a powerful tool for imaging spectroscopy (3D-scans).
IR Detectors and Cameras
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The Gemini Near-Infrared Imager (NIRI): a discussion of its design features and performance
Klaus-Werner Hodapp, Everett M. Irwin, Hubert Yamada, et al.
The Gemini Near-Infrared Imager (NIRI) has now been completed and is in operation at the telescope. This paper discusses the basic design of the instrument and a number of particularly interesting technical issues. NIRI offers three different pixel scales to match different operating modes of the Gemini telescope and allows polarimetric and spectroscopic observations. It is equipped with an infrared wavefront sensor to allow tip-tilt correction even in highly obscured regions.
Near-infrared coronagraph imager on the Subaru 8 m telescope
Koji Murakawa, Hiroshi Suto, Motohide Tamura, et al.
We introduce a near-infrared camera named coronagraph imager with adaptive optics (CIAO) mounted on the Subaru 8m telescope. Combined with the Subaru 36 elements adaptive optics (AO), CIAO can produce nearly diffraction limited image with approximately 0.07 arcsec FWHM at K band and high dynamic range imaging with approximately 10 mag difference at 1 arcsec separation under typical seeing conditions. We have carried out performance tests of imaging without and with coronagraph mask since its first light observation held on 2000 February. Because of limited weather conditions, the performance under best seeing conditions has not been tested yet. At a typical natural seeing condition of 0.4 - 0.8 arcsec, halo component of PSF using 0.2 - 0.8 arcsec mask can be reduced up to 70% comparing with that without mask using AO. Even after correction, residual wave front error has typically 1.2 rad2 which corresponds to the Strehl ratio of approximately 0.3 at K band. Such wave front errors degrades the image quality; this is a common problem of coronagraph on the ground-based telescope with non high-order AO. Nevertheless we emphasize that there are various advantages on our coronagraph: the clean PSF of CIAO, reduction of readout noise, and less effect of detector memory problem. Compared with coronagraphs on smaller telescopes, the PSF shape is sharper and it brings higher detectability of sources around bright objects.
Near infrared coronagraphic imager for Gemini South
The Near Infrared Coronagraphic Imager for Gemini South (NICI) is a dual beam coronagraphic camera operating over the 1.0 to 5.5 micrometer wavelength range with a dedicated adaptive optics system. NICI target science, design and capabilities will be described as an introduction to this instrument slated for deployment in mid 2005.
UFTI: the 0.8-2.5 µm fast-track imager for the UK Infrared Telescope
Patrick F. Roche, Philip W. Lucas, Craig D. Mackay, et al.
In 1996, it was proposed to build a near-infrared imager for the 3.8-m UK Infrared Telescope in Hawaii, to exploit the 1024 pixel format detectors that were then becoming available. In order to achieve a fast delivery, the instrument was kept simple and existing designs were reused or modified where possible. UFTI was delivered within 2.5 years of the project start. The instrument is based around a 1k Rockwell Hawaii detector and a LSR Astrocam controller and uses the new Mauna Kea optimized J,H,K filter set along with I and Z broad-band filters and several narrow-band line filters. The instrument is cooled by a CTI cry-cooler, while the mechanisms are operated by cold, internal, Bergelahr stepping motors. On UKIRT it can be coupled to a Fabry-Perot etalon for tunable narrow-band imaging at K, or a waveplate for imaging polarimetry through 1-2.5 μm; the cold analyzer is a Barium Borate Wollaston prism. UFTI was designed to take full advantage of the good image quality delivered by UKIRT on conclusion of the upgrades program, and has a fine scale of 0.09 arcsec/pixel. It is used within the UKIRT observatory environment and was the first instrument integrated into ORAC, the Observatory Reduction and Acquisition Control System. Results obtained during instrument characterization in the lab and over the last 3 years on UKIRT are presented, along with performance figures. UFTI has now been used on UKIRT for several hundred nights, and aspects of instrument performance are discussed.
CanariCam: a multimode mid-infrared camera for the Gran Telescopio CANARIAS
Charles M. Telesco, David Ciardi, James French, et al.
The University of Florida is developing a mid-infrared camera for the 10.4-meter Gran Telescopio CANARIAS. CanariCam has four science modes and two engineering modes, which use the same 320 x 240-pixel, arsenic-doped silicon, blocked-impurity-band detector from Raytheon. Each mode can be remotely selected quickly during an observing sequence. The pixel scale is 0.08 arcsec, resulting in Nyquist sampling of the diffraction-limited point-spread-function at 8 μm, the shortest wavelength for which CanariCam is optimized. The total available field of view for imaging is 26 arcsec x 19 arcsec. The primary science mode will be diffraction-limited imaging using one of several available spectral filters in the 10 μm (8-14 μm) and 20 μm (16-25 μm) atmospheric windows. Any one of four plane gratings can be inserted for low and moderate-resolution (R = 100 - 1300) slit spectroscopy in the 10 and 20-μm regions. Insertion of appropriate field and pupil stops converts the camera into a coronagraph, while insertion of an internal rotating half-wave plate, a field mask, and a Wollaston prism converts the camera into a dual-beam polarimeter.
Characterication in the laboratory of VISIR, the mid-infrared imager and spectrometer for the VLT
Pierre-Olivier Lagage, Jan-Willem Pel, Arnaud Claret, et al.
In this paper, we present the status of VISIR, the mid-infrared instrument to be installed in 2003 at the Cassegrain focus of MELIPAL, one of the four 8-meter telescopes of the European Very Large Telescope. This cryogenic instrument, optimized for diffraction-limited performance in both mid-infrared atmospheric windows (N and Q band), combines imaging capabilities over a field up to about 1x1 arcmin2, and long-slit (0.5 arcmin) grating spectroscopy with various spectral resolutions up to R=25000 at 10 μm and 12500 at 20 μm. The contract to design and build VISIR was signed in November 1996 between the European Southern Observatory (ESO) and a French-Dutch consortium of institutes led by Service d'Astrophysique of Commissariat l'Energie Atomique (CEA). A key step in the project has been passed in December 2001, with the first infrared images in the laboratory and in April 2002 with the first infrared spectra in the laboratory. We present the results of the laboratory tests of the instrument, which is scheduled to be shipped to Paranal at the end of 2002.
Optical Spectrograph I
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Progress toward science results with the ACES spectrograph
The use of spectrographs with telescopes having high order adaptive optics (AO) systems offers the possibility of achieving near diffraction-limited spectral resolution on ground-based telescopes, as well as important advantages for instrument design. The small stellar image diameters obtained with adaptively corrected systems allow high resolution without a large loss of light at the spectrograph entrance slit, as well as greater spectral coverage per exposure. The adaptively corrected echelle spectrograph (ACES), designed at Steward Observatory for a spectral resolution R ≈ 200,000, couples the telescope pupil to the instrument with a 10 mm diameter near single-mode optical fiber. Initial observations at the 2.5m telescope on Mt. Wilson validated the concept of achieving high spectral resolution with an adaptively corrected telescope and fiber coupled spectrograph. However the transmission of multiple modes in the fiber lead to a wavelength-dependent variation in illumination that made flat fielding impossible. In this paper we describe instrument design improvements, the installation and testing of a new CCD detector, and testing aimed at understanding and eliminating the fiber-related transmission problems to permit science quality imaging.
Optical Detectors and Cameras
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SIDECAR low-power control ASIC for focal plane arrays including A/D conversion and bias generation
Markus Loose, L. Lewyn, Hakan Durmus, et al.
Large two-dimensional imaging arrays, spanning infrared focal plane arrays through visible CCDs, usually require extensive support electronics. We present an application specific integrated circuit (ASIC) that combines, on a single chip, all necessary functions to operate CMOS-based focal plane arrays and provide digital data from 12 to 16 bits. The interface to the external world is completely digital, thus eliminating the complexity of dealing with sensitive analog voltages. The ASIC's first application is for use with the HAWAII-2RG (a 2048 x 2048 multiplexer specifically optimized for the Next Generation Space Telescope). Due to its flexibility, it can control other FPAs and SCAs not requiring clocks or biases higher than 3.3 V. The low-power, system-on-chip controller comprises a 16-bit microcontroller, program and data memory, clock generator, bias generator, 36 programmable gain amplifiers (0 to 27 dB), thirty-six 12-bit 10 MHz A/D converters, thirty-six 16-bit 500 kHz A/D converters, glue logic and programmable I/O pads. When configured for NGST, we estimate ≤ 8.4 mW continuous power for the 2k x 2k FPA and ASIC. The programmable ASIC, dubbed SIDECAR, for System for Image Digitization, Enhancement, Control And Retrieval, is likely an optimum "back-end" solution for other high-performance instruments.
IR Detectors and Cameras
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Optical design of WIRCAM the CFHT wide-field infrared camera
Simon Thibault, Qingfeng Cui, Michel Poirier, et al.
In this paper, we present the final design of the optical train of WIRCAM, a wide-field infrared camera to be installed in early 2004 at the prime focus of CFHT. This cryogenic camera, optimized for J, H and K operating region, used a 4k x 4k IR detector mosaic fed by a single optical train. The sky will be imaged onto the focal plane at an optical speed of F/3.5 yielding an image scale of 0.3 arcsecond per 18 μm pixel. The design image quality is 0.30 arcsecond 50% diffraction encircled energy over the central 20 arcmin field and no images worse than 0.35 arcsecond over the 29.7 arcminute diameter camera field. The optical design distortion at the corners is less than 1%. The WIRCAM camera have a lyot stop at the telescope image pupil in order to mask background radiation coming from external structures. The image of the pupil is sufficiently sharp for background elimination and impose not more than 2% loss of light from the sky in the K spectral band. We also present an optimization of AR coating for IR based camera weighted by MK atmospheric transmission. We discuss the impact of this coating design method on various camera throughput. We include an efficient technique for ghost analysis based on the detector image. We demonstrate that our design meets the performance requirements from an optical and practical point of view.
IR Spectrographs I/Cameras I
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IRMOS: an infrared multi-object spectrometer using a MEMs micromirror array
The Infrared Multi-Object Spectrometer (IRMOS) is an innovative near-IR instrument approaching completion. IRMOS will provide R~300, 1000, and 3000 spectroscopy in the J, H, and K bands plus R~1000 in Z together with imaging in all bands. Using a Texas Instruments 848x600 element DMD as a micro mirror array to synthesize slits in an imaging spectrometer obtaining up to 100 simultaneous spectra will be possible. Designed for the KPNO 4 and 2.2 meter telescopes, IRMOS will provide 3x2 and 6x4 arc minute fields of view on these telescopes. IRMOS is constructed mainly of 6061 Aluminum using diamond machined optics which has permitted a complex, compact, all reflective optical design. We describe the design and status of IRMOS, summarize its expected performance, and discuss several interesting aspects of its development and the use of TI DMD devices. IRMOS is a joint project of the Space Telescope Science Institute, the NASA Next Generation Space Telescope Project, and the Kitt Peak National Observatory.
LUCIFER: a multimode NIR instrument for the LBT
Walter Seifert, Immo Appenzeller, Harald Baumeister, et al.
LUCIFER (LBT NIR-Spectroscopic Utility with Camera and Integral-Field Unit for Extragalactic Research) is a NIR spectrograph and imager for the Large Binocular Telescope (LBT) on Mt. Graham, Arizona. It is built by a consortium of five German institutes and will be one of the first light instruments for the LBT. Later, a second copy for the second mirror of the telescope will follow. Both instruments will be mounted at the bent Gregorian foci of the two individual telescope mirrors. The final design of the instrument is presently in progress. LUCIFER will work at cryogenic temperature in the wavelength range from 0.9 μm to 2.5 μm. It is equipped with three exchangeable cameras for imaging and spectroscopy: two of them are optimized for seeing-limited conditions, the third camera for the diffraction-limited case with the LBT adaptive secondary mirror working. The spectral resolution will allow for OH suppression. Up to 33 exchangeable masks will be available for longslit and multi-object spectroscopy (MOS) over the full field of view (FOV). The detector will be a Rockwell HAWAII-2 HgCdTe-array.
The Fiber Multi-Object Spectrograph (FMOS) for the Subaru Telescope
Masahiko Kimura, Toshinori Maihara, Kouji Ohta, et al.
The Fibre Multi-Object Spectrograph (FMOS) is a second-generation common-use instrument of the Subaru telescope. Under an international collaboration scheme of Japan, UK, and Australia, a realistic design of FMOS has been already in completion, and the fabrications of hardware components have been in progress. We present the overall design details together with the special features of FMOS subsystems, such as the prime focus corrector, the prime focus mechanical unit including fiber positioners, and the near-infrared spectrograph, etc.
Poster Session B
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Optical fiber link between OzPoz, GIRAFFE, and UVES (FLAMES project)
The FLAMES project is the VLT Fibre Facility. It includes the fibre positioner OzPoz linking the GIRAFFE and UVES spectrographs. FLAMES is located on the Nasmyth Platform A of the Kueyen VLT telescope. The optical fibre link is arranged in four bundles: the Medusa system with 132 single fibres for multi-object spectroscopy, 15 deployable IFU modules for integral field spectroscopy of small objects, the Argus large integral field unit with two possible samplings and a bundle of 8 fibres and 55 m long linking OzPoz to UVES, a high resolution spectrograph situated on the opposite Nasmyth platform. This paper describes the final characteristics and performances of all the fibre bundles and the status at their installation at the telescope.
Breakthroughs in silicon grism and immersion grating technology at Penn Stat Univ
Jian Ge, Daniel Ludlow McDavitt, Shane Miller, et al.
Fabrication of silicon grisms up to 2 inches in dimension has become a routine process at Penn State thanks to newly developed techniques in chemical etching, lithography and post-processing. The newly etched silicon grisms have typical rms surface roughness of ~ 9 nm with the best reaching 0.9 nm, significantly lower than our previous attempts (~ 20-30 nm). The wavefront quality of the etched gratings is high. Typical wavefront error is ~ 0.035 wave at 0.6328 micron, indicating diffraction-limited performance in the entire infrared wavelengths (1.2-10 microns) where silicon has excellent transmission. These processes have also significantly eliminated visible defects due to grating mask breaks during chemical etching. For the best grisms, we have less than 1 defect per cm2. The measured total integrated scatter is less than 1% at 0.6328 micron, indicating similar or lower scatter in the IR when grisms are operated in transmission. These new generation grisms are being evaluated with our Penn State near IR Imager and Spectrograph (PIRIS) in cryogenic temperature. We are applying the new techniques in etching an 80x40 mm2 grating on 30 mm thick substrate to make an anamorphic silicon immersion grating, which can provide a diffraction-limited spectral resolution of R = 220,000 at 2.2 micron. We plan to put this immersion grating in a modified PIRIS to measure magnetic field strength using the Fe I line at 1.56 micron among hundreds of nearby solar type stars to investigate the probability of the Maunder Minimum using the Mt. Wilson 100inch with adaptive optics in 2003.
Development of a mid-infrared high-dispersion spectrograph (IRHS) for the Subaru Telescope
Hitoshi Tokoro, Masashi Atarashi, Masako Omori, et al.
A design of prototype Infra-Red High-dispersion Spectrograph (IRHS) is described. IRHS is a cryogenic echelle spectrometer for 8.2-m Subaru Telescope, which will operate at 8 to 13 μm with resolving power of 200,000. To achieve such a high dispersion and broad bandwidth, a Germanium immersion echelle grating was adopted. As a preliminary step, we started to develop the proto-type of IRHS (ProtoIRHS) with currently available Ge immersion grating (30x30x72 mm) and one 512x412 Si:As impurity band detector array, which will provide the maximum resolving power of 50,000 at 10 μm with slit width of 0.612 arcseconds (0.48 mm) and two-pixels sampling.
Cross-dispersion and an integral field unit for Hectochelle
We describe our plans to add cross-dispersion and an integral field unit to the Hectochelle spectrograph, a multiobject, fiber-fed echelle spectrograph for the converted MMT. Hectochelle was originally designed without cross-dispersion to be used in a single order or overlapping orders selected by interference filters. The addition of cross-dispersion allows us to trae off multiplex advantage for spectral coverage. Our cross-disperser uses an unusual segmented, zero-deviation prism that is very compact, allowing it to fit into the existing instrument without modification. The planned integral field unit can be used with either Hectochelle or the moderate-dispersion Hectospec bench spectrograph. Both spectrographs were originally designed to be fiber-fed with a robotic fiber positioner as a front end, so adding an integral field capability is a natural enhancement. The integral field unit will use smaller diameter fibers than the robotic fiber positioner (subtending 0".6 vs. 1".5), so that both spectrographs will achieve higher spectral resolution in integral field mode. With the integral field unit Hectochelle will reach a two pixel resolution, R approximately 70,000, and Hectospec will reach R approximately 2000 with its 270 line mm-1 grating.
The Hobby-Eberly telescope medium resolution spectrograph and fiber instrument feed
Lawrence W. Ramsey, Leland G. Engel, Nicholas Sessions, et al.
The Medium Resolution Spectrograph (MRS) is a versatile, fiber-fed echelle spectrograph for the Hobby-Eberly Telescope (HET). This instrument is designed for a wide range of scientific investigations and includes single-fiber inputs for the study of point-like sources, synthetic slits of fibers for long slit spectroscopy 9 independently positionable probes for multi-object spectroscopy, and a circular fiber integral field unit. The MRS consists of two beams. The visible beam has wavelength coverage from 450 - 900 nm in a single exposure with resolving power between 5,300 and 20,000 depending on the fibers configuration selected. This beam also has capability in the ranges 380 - 950 nm by altering the angles of the cross-disperser gratings. A second beam operating in the near-infrared has coverage of 900 - 1300 nm with resolving power between 5,300 and 10,000. Both beams can be used simultaneously and are fed by the HET Fiber Instrument Feed (FIF) which is mounted at the prime focus of the telescope and positions the fibers feeding the MRS. The MRS started commissioning summer 2002.
Performance verification of HARPS: first laboratory results
The high-resolution spectrograph HARPS (High-Accuracy Radial-velocity Planet Searcher) will be installed on the 3.6m telescope at the ESO La Silla Observatory towards the end of 2002 and offered to the astronomical community by mid-2003. Assembly and integration of the instrument took place at the Geneva Observatory, Switzerland, during Spring 2002. At present, the verification of the system performance is in progress and is already in an advanced phase. We present in this paper the first results of our laboratory tests and describe various performance figures. We stress the outstanding mechanical and thermal stability of the instrument which are crucial for accurate radial velocity measurements. We also give a description of the simultaneous ThAr-reference technique which ensures an overall efficiency 6 times higher than with an the iodine cell absorption method. The combination of the high instrumental stability with the simultaneous ThAr-reference technique provides HARPS with characteristics highly adapted for accurate radial-velocity determination at the level of 1 ms-1. These make our instrument suitable for the detection of planetary systems and of extra-solar planets with sub-saturnian mass.
Commissioning of the PMAS 3D spectrograph
Andreas Kelz, Martin M. Roth, Thomas Becker
PMAS, the Potsdam Multi-Aperture Spectrophotometer, was successfully commissioned at the Calar Alto 3.5m telescope during 2001. PMAS is a medium-resolution, lensarray/fiber based integral field spectrograph, covering the whole optical wavelength range from 350 to 900 nm with optimized high efficiency in the blue. We review the commissioning activities and present the current status of this new instrument.
Visible Imaging Fourier Transform Spectrometer: Design and Calibration
Edward H. Wishnow, Ronald E. Wurtz, Sebastien Blais-Ouellette, et al.
We present details of the design, operation and calibration of an astronomical visible-band imaging Fourier transform spectrometer (IFTS). This type of instrument produces a spectrum for every pixel in the field of view where the spectral resolution is flexible. The instrument is a dual-input/dual-output Michelson interferometer coupled to the 3.5 meter telescope at the Apache Point Observatory. Imaging performance, and interferograms and spectra from calibration sources and standard stars are discussed.
Integral field unit for the echellette spectrograph and imager at Keck II
Andrew I. Sheinis, Lee Laiterman, David F. Hilyard, et al.
We present the design and status report on the development of an Integral Field Unit (IFU) for the Echellette spectrograph and imager (ESI), a recently developed R=13000, Cassegrain spectrograph at Keck II. We have designed a family of IFU’s for the spectrograph, providing a range of field-coverages and dispersions. The optical designs are based on the Advanced Image Slicer concept of Content. We describe the completely monolithic, passive, and modular implementation of this design as an IFU head. Each IFU head resides in an ESI slit mask holder, so that it is completely selectable/deselectable as an observing mode during a nights observing run.
SIFUS: SOAR integral field unit spectrograph
Jacques R. D. Lepine, Antonio Cesar de Oliveira, Milito Vieira Figueredo, et al.
We present the project of an optical spectrograph equipped with a 1300-element Integral Field Unit (IFU), that will be one of the main instruments of the SOAR (4m) telescope. The instrument consists of two separate parts, the fore-optics and the bench spectrograph, that are connected by an 11 m long fiber bundle. The fore optics system is installed at one of the Nasmyth focii of the telescope, and produces an image of the observed object on a 26x50 array of square microlenses, each 1 mm x 1 mm lens feeding one fiber. The fibers have 50 micron cores, and are aligned at the entrance of bench spectrograph to form a slit that feeds a 100 mm beam collimator. A set of Volume Phase-Holographic (VPH) transmission gratings can be interchanged by remote control, providing a choice of resolution and wavelength coverage. The spectrograph is tunable over the wavelength range 350 to 1000 nm, with resolution R from about 5000 to 20000. This spectrograph is ideally suited for high spatial resolution studies, with a sampled area of the sky 8" x 15", with 0.30" per microlens, in the mode to be used with the tip-tilt correction of SOAR. The project has been approved at the Project Design Review and the spectrograph is presently being constructed.
MUSE: a second-generation integral-field spectrograph for the VLT
Francois Henault, Roland Bacon, Christophe Bonneville, et al.
We describe MUSE (Multi Unit Spectroscopic Explorer), a second-generation integral-field spectrograph for the VLT, operating in the visible and near IR wavelength range. It combines a 1' x 1' Field of View with the improved spatial resolution (0.2") provided by adaptive optics and covers a large simultaneous spectral range (0.48 - 1 μm). With this unique combination of capabilities, MUSE has a wide domain of application, and a large discovery potential. It will provide ultra deep fields with a limiting magnitude for spectroscopy of R = 28. After a brief presentation of the scientific case and the derived instrument requirements, we will focus on the MUSE optical design, including the overall architecture, the major trade-off that were conducted in order to optimize the cost and performance, and a provisional implementation scheme of the instrument on the VLT Nasmyth platform. Then the most important optical subsystems (as the 3 x 8 Field-splitter, the Image Slicers and the Spectrometers) are described. One of MUSE special feature is the impressive number of Image Slicer and Spectrometer modules which must be manufactured, that is 24. The realization of such series has been studied in collaboration with an industrial company. Finally a preliminary estimation of the expected performance and a technological development program in order to secure the realization of the critical optical subsystems will be presented.
Developments on the UK FMOS project for the Subaru Telescope
Ian J. Lewis, Gavin B. Dalton, Alan R. Holmes, et al.
We describe the UK participation in the FMOS project to provide multi-object IR spectroscopy for the Subaru telescope. The UK is working on the design of an OH suppression IR spectrograph, this work comprises the optical design, the opto-mechanical layout, spectrograph thermal environment and cryogenics and detector control system. We give a progress report on the current design work.
Design and commissioning of a dual visible/near-IR echelle spectrograph for the AEOS telescope
Robert J. Thornton, Jeff R. Kuhn, Klaus-Werner Hodapp, et al.
The Institute for Astronomy has developed and recently installed a high-resolution cross-dispersed echelle spectrograph for use at one of the coudé foci of the AEOS 3.7-meter telescope, operated by the Air Force Space Command atop Mt. Haleakala on the island of Maui. The spectrograph features an optical arm for the wavelength range 0.5 - 1.0 μm and an infrared arm for the range 1.0 - 2.5 μm. We review the spectrograph design and present commissioning results obtained with both the visible and infrared arms. Both channels use a white-pupil collimator design to maximize grating efficiency and to limit the size of the camera optics. The visible arm of the spectrograph uses deep-depletion CCDs optimized for operation near 1.0 μm. The infrared detector is a 2048 x 2048 HgCdTe array (HAWAII-2) that has been developed by the Rockwell Science Center for this project. Both channels are equipped with slit-viewing cameras for object acquisition and control of a fast guiding tip-tilt mirror located at a pupil image in the spectrograph fore optics.
The LAMOST multi-object spectrographs with aspherized gratings
LAMOST is a powerful spectra survey telescope with 4 meter aperture and 5 degree FOV. Its focal plate with 1.75 meter diameter can accommodate 4000 fibers in which feeds 16 multi-object spectrographs. In the last conference of astronomical telescope and instrumentation hold in Munich, Germany in April, 2000, preliminary design for LAMOST multi-object spectrographs based on plane reflective gratings and Schmidt camera with refractive corrector has been reported. Here, use aspherized reflective grating instead of the plane reflective grating and need for refractive corrector plate is avoided. Compared to previous design using a refractive plate for correcting aberrations from both collimator and camera mirror, use of aspherized grating has the achromaticity advantage as well as less asphericity, and minimizes the number of optical surface. This would improve the efficiency of spectrograph and allows much broader spectral coverage. In this paper, we present the current design of multi-object spectrographs for LAMOST project.
Development of binospec and its optics
Daniel G. Fabricant, Harland W. Epps, Warren L. Brown, et al.
Binospec is a binocular optical spectrograph under development for the converted MMT. Binospec addresses two adjacent 8' by 15' fields of view, yielding an effective slit length of 30'. Despite its very wide field of view, Binospec's optics are compact due to the favorable image scale at the converted MMT's f/5 Cassegrain focus. However, Binospec's all-refractive collimator and camera have presented several challenges, including the need for careful athermalization and high performance optics mounts. In the course of Binospec's development H.W.E. and D.G.F. developed a new athermalization technique to maintain image scale, image quality, and focus over a wide temperature range using thin lenses formed in the coupling fluid between lens multiplets. Tight specifications for image quality and gravity-induced image motion and defocus lead to tight specifications for displacements of Binospec's optical elements. We describe how Binospec's elastomeric lens mounts have been tuned to attain this level of performance.
ARCES: an echelle spectrograph for the Astrophysical Research Consortium (ARC) 3.5-m telescope
Shu-i Wang, Roger H. Hildebrand, Lewis M Hobbs, et al.
A new echelle spectrograph was commissioned in 1999 for the ARC 3.5 meter telescope. The key features of the instrument are that it has a resolution of 9 km/sec, limited by the pixel size of the CCD; has no moving parts behind the slit during observation; provides complete spectral coverage from 3200A to 10000A, limited by the prism cross disperser material on the blue side and by the CCD sensitivity on the red side; provides blazeless spectra; achieves S/N>3000; and is remotely operable. The instrument is being used for studies of abundances in stars and for a large survey of diffuse interstellar bands.
High-resolution fibre-fed echelle spectrograph for the Southern African Large Telescope
Stuart I. Barnes, John B. Hearnshaw, Peter Cottrell, et al.
The design of the Canterbury Extremely Large Echelle Spectrograph on the Telescope In Africa (CELESTIA) is currently in progress. This high-resolution fiber-fed echelle spectrograph will be used with the Southern African Large Telescope (SALT) which is currently under construction at the South African Astronomical Observatory, near Sutherland, South Africa. CELESTIA uses a mechanically aligned mosaic of two 304 x 408-mm echelle gratings, and cross-dispersion is achieved using two large prisms in double-pass. An extremely fast (f/0.65 in white light, f/2.2 in monochromatic light) camera with all-spherical surfaces based on the design of Epps and Vogt for Keck HIRES has been adapted for this spectrograph. The dispersive elements of CELESTIA may be placed in a helium-filled chamber with the first element of the camera serving as an optical window. A range of resolving powers from 23000 to 100000 will be possible with fibers having diameters of 300 to 400 μm and various combinations of fiber-exit micro-slits. It is possible to image the spectrum of a second object, the sky, or a calibration lamp at most resolving powers. Complete spectral coverage from 380 nm to 670 nm, and nearly complete coverage to 880 nm is possible with a mosaic of two 30.7 x 61.4-mm detectors. Some details of the expected performance of CELESTIA are presented. It is expected that the spectrograph will have a maximum efficiency of approximately 20%, not accounting for the atmosphere or telescope. This compares favorably with other existing spectrographs designed for large telescopes.
Fiber fed spectral calibration with the Hobby-Eberly telescope
The Hobby-Eberly Telescope (HET) imposes unique constraints on the design of a spectral calibration system. Its 9.2 m aperture and queue scheduled operation make traditional dome screens impractical. Furthermore, the changing pupil of the HET's tilted Aricebo design is far more drastic than the simple rotation of traditional alt-azimuth telescopes. Given these constraints we elected to build an internal spectral calibration system (SCS) common to all instruments. The SCS can feed all HET instruments from a uniformly illuminated Lambertian screen located within the spherical abberation corrector (SAC) at the telescope's second pupil. A moving baffle installed at the third pupil will reproduce, during calibration, the actual HET pupil seen in a science exposure. We eliminated all heat sources at the SAC by locating the lamps in the basement below the telescope and coupling source to screen through 12 600 μm diameter 35 m long fibers.
The performance of OzPoz: a multifiber positioner on the VLT
Peter R. Gillingham, Dan Popovic, Tony J. Farrell, et al.
OzPoz is a multi-fiber positioner to feed spectrographs from a Nasmyth focus of VLT Unit Telescope 2. The concept follows that of the 2dF system on the AAT: a robot re-positions magnetically attached buttons on one of a pair of steel plates while the other plate is observing. But the large scale and the curvature of the VLT Nasmyth focal surface led to the design being very different. Its combination of large moving elements with high precision and the need to survive severe earthquakes presented special challenges. Electrical interlocking of the many functions had to be very comprehensive to minimize risks of damage to the instrument and harm to personnel. Despite the valuable inheritance from 2dF, considerable effort had to be devoted to software to fit the ESO VLT environment and to deal with the complexity of the interacting elements. Integration on the VLT commenced in March 2002, followed by commissioning runs with Giraffe in June, August, and October. Some instrument defects were uncovered during installation and commissioning but none was fundamental and they were readily fixed in between night runs. The time taken to reconfigure a plate, an average of ten seconds/fiber, meets specification and the accuracy of alignment of fiber apertures with stars is limited mostly by the astrometry of target fields.
Multi-object spectroscopy of FOCAS: software and its performance
Yoshihiko Saito, Youichi Ohyama, Nobunari Kashikawa, et al.
Faint Object Camera and Spectrograph, FOCAS, is a Cassegrain versatile optical instrument of Subaru telescope. Among various observing modes of FOCAS, the multi-object spectroscopy (MOS) requires dedicated software suite which enables accurate positioning of masks which have over fifty slitlets on faint targets over 6 arcminutes diameter field-of-view (FOV). We have been developing three kinds of software: the image processing software performing combining mosaic CCD images and optics distortion correction, mask designing program (MDP) for the slit arrangement, and pointing offset calculator (POC) for the target acquisition on slits. MDP and POC provide observers a graphical user interface (GUI) for efficient and quick mask designing and target acquisition. Our test has shown that the slit positioning accuracy on targets is about 0.2 arcsec RMS over entire FOV, and is accurate enough for typical observations with 0.4 arcsec slits or wider. We briefly describe our software as well as the pointing accuracy and the required time for the MOS target acquisition with FOCAS.
The Gemini-North multi-object spectrograph stability performance
Richard G. Murowinski, Jeremy R. Allington-Smith, Steven M. Beard, et al.
Of the Gemini Multi-Object Spectrograph's (GMOS) scientific requirements, one which led to technically interesting areas was the ability to measure velocities to an accuracy of 2km/s over the entire 5.5 arcminute square field. GMOS's design to meet this requirement includes a mechanical design for stiffness and without hysteresis or image rotation, and an open loop flexure control system which translates the detector position to compensate for flexure. The model used to predict the flexure is an empirical one developed from measured flexure results. In this paper we present the analysis of factors which enable meeting the 2km/s requirement, and the observing strategies needed to make those observations. We look in particular detail at the development and test of that flexure compensation system, including both lab results and on-telescope results.
Cryogenic Fabry-Perot spectrometer for the near infrared
Alexander S. Kutyrev, Charles Leonard Bennett, Samuel Harvey Moseley Jr., et al.
We have designed and built a high spectral resolution cryogenic double Fabry-Perot infrared spectrometer to survey the diffuse emission of ionized hydrogen (Br γ line) in the Galactic plane. In the initial survey, presented here, we employed the non-imaging mode of the spectrometer to achieve the best possible sensitivity for the faint diffuse emission. The emission measure detection limit was about 300 cm-6pc. The resolving power of the instrument is 104 and the simultaneous velocity range is approximately 200 km s-1. The spectrometer consists of a liquid nitrogen cryostat, which accommodates Fabry-Perot interferometers and a liquid helium cryostat for the InSb 256 x 256 detector. Each Fabry-Perot interferometer is located in a separate chamber in the cryostat. Tuning of the spectrometer is accomplished by varying the pressure of dry nitrogen gas in the chamber. The cold shields of the spectrometer and the detector cryostat are connected. Stray radiation is reduced by use of a cold stop, with the appropriate relay optics, located between the cryostats. This design limits stray background radiation and thermal radiation from the spectrometer itself, greatly improving the detection limit of the system. All of these design features maximize experiment sensitivity, which is limited by thermal emission from outside of the spectrometer, and by variation of the atmospheric emission lines.
Developing a new data acquisition devices for COMICS
We developed a new data acquisition device for COMICS, a mid infrared instrument of the Subaru telescope. The new device was installed in place of our previous data acquisition device with a lower data transfer speed. The new device is 32 bit PCI bus and PC Linux based and provides bus-master DMA transfer function. It consists of a clock pattern generator, frame memories, and an image co-adder. In order to achieve high operational efficiency for mid infrared instruments, the data handling speed is essential as well as the speed of A/D converter. The data transfer to the hard disk drive on the PC is made during acquiring the data at the rate higher than the data generation rate. As a result, we succeeded to reduce the dead time due to the data transfer procedure from 60 sec to less than 1 sec for 200 frames (64M bytes). Furthermore by replacing the host computer by a higher performance PC, the observation efficiency of COMICS was improved from 44% to 74% in the imaging mode. This PCI based data acquisition device can also be applied to the other instruments that have fast data rates.
Properties of FOCAS optical components
The Faint Object Camera and Spectrograph, FOCAS, is a Cassegrain optical instrument of Subaru telescope. For its versatility, FOCAS has many optical components such as grisms, filters, and polarizers. They are inserted in the collimated beam section of 451 mm length. For the large pupil (90 mm in diameter) and the wide field of view (6 arcmin in diameter) of FOCAS, rigorous efforts were made in developing, manufacturing and assembling these components. The resultant performance of the instrument is quite stable and is almost as high as that expected from the design values. In the text, overall characteristics of each optical element is described.
OSIRIS optics
The optics of OSIRIS, a versatile first generation imager/spectrograph, for the 10.4-m Gran Telescopio Canarias (GTC), has undertaken its manufacturing phase. Brief descriptions of the design characteristics and expected performance are given. Current advances in a relevant optical study (throughput) are summarized as well as the status of manufactured lenses. A comparison with similar instruments for 6.5-m to 10-m class telescopes is performed, based on the instrument pupil size, collimator focal length, angular magnification, required field of view (FOV) and Lagrange Invariant. We finish with the compliance matrix of the top-level requirements, showing that OSIRIS represents a so far unique scientific opportunity of tunable imaging in this telescope class.
Optics of the instrument Elmer for the GTC 10-m telescope (Gran Telescopio CANARIAS)
Elmer is a visible imager and spectrograph for the Gran Telescopio Canarias, which has been designed in-house. The major features and some of the analysis done are shown for each optical assembly. The image error budget is presented with the current estimations, as well as the foreseen acceptance tests. Finally the present status of the optics is presented.
Design and performance of the SOAR primary mirror calibration wavefront sensor
Allan Wirth, Jennifer Roberts, Thomas Gonsiorowski, et al.
Adaptive Optics Associates has designed and built the Southern Astrophysical Research (SOAR) telescope primary mirror calibration wavefront sensor. It will be used to monitor the figure of the active primary mirror during observations. The package also includes an acquisition camera subsystem. The sensor uses many commercial components to control cost while meeting the desired technical specifications. We describe the wavefront sensor system and present results of performance testing obtained in the laboratory.
Thermal considerations in modern spectrograph design: the Binospec spectrograph
We have completed a detailed thermal analysis of Binospec, a wide-field, multi-slit spectrograph being developed for the 6.5m MMT. The goals of our analysis were to minimize temperature gradients and thermally-induced deflections and achieve a > 24 hr time constant in the spectrograph optics. We consider the effects of conduction, convection, and radiation with the external environment, and model the consequences of opening a spectrograph to insert new slit masks or filters. We study when internal heat sources balance environmental effects, and the local effects of a hot motor in a spectrograph. We review the results of these thermal analyses and draw general conclusions useful to instrument builders.
An image motion compensation system for the multi-object double spectrograph
Jennifer L. Marshall, Bruce Atwood, Paul Laurence Byard, et al.
We describe a closed-loop image motion compensation system (IMCS) for the Multi-Object Double Spectrograph (MODS). The IMCS compensates for structural bending due to gravity and eliminates image motion from temperature fluctuation and mechanism flexure within the instrument during an observing period. The system makes use of an infrared laser source at the telescope focal plane, which produces reference spots in the science detector plane. Movement of these spots accurately tracks science image motion, since the two beams share a common optical path. Small real-time adjustments to the position of the MODS collimator mirror compensate for the image motions.
Preliminary optical design for the Flamingos-2 near-infrared multi-silt spectrograph and imager for Gemini-South
Harland W. Epps, Richard Elston
The University of Florida previously designed and implemented a fully-cryogenic near-infrared multi-object (slit) spectrograph and imager called Flamingos which has been used successfully at the f/8.0 Cassegrain focus of the Kitt Peak 4.0-m telescope and elsewhere. Current plans are under way to design an to build a similar but larger, more efficient follow-on near-infrared instrument to be used at the f/16.0 focus of the 8.0-m Gemini-South telescope. The new design is called Flamingos-2. It will accommodate the (1.00 to 2.40)-micron wavelength range for grism-driven spectroscopy and it will provide direct imaging in the customary J-, H- and K-band(s). It will feature a 100.0-mm diameter collimated beam and it will reimage at 100.0 microns/arcsec upon a flat RSC Hawaii-2 (2048 by 2048 by 18-micron) array. We have designed preliminary all-refracting, all-spherical cryogenic optics for Flamingos-2. Near-infrared optical material alternatives are discussed. The importance of using low-index materials is emphasized. Our 6-element collimator contains only one high-index (ZnSe) element. Our 6-element camera contains no high-index element. It uses a medium-index near-infrared transmitting optical glass which provides excellent color correction. We present these fully-quantitative preliminary optical designs for Flamingos-2 together with our anlaysis of its expected performance for spectroscopy and for direct-imaging applications.
Cryogenic MOS unit for LUCIFER
We present a system for the exchange and handling of cold field masks in LUCIFER, the near infrared camera and spectrograph for the LBT. Inside the LUCIFER cryostat, 10 field-stop and long-slit masks, and 23 multi-slit masks are stored in a stationary and an exchangeable cabinet respectively. With LUCIFER at operating temperature, the exchangeable cabinet with its multi-slit masks can be transferred from the LUCIFER cryostat to an auxiliary cryostat, and a second cabinet harboring the newly made, pre-cooled masks can be transferred back to LUCIFER from a second auxiliary cryostat. Inside LUCIFER, a robot transports the individual masks from their storage position in the cabinet to the focal plane and inserts them in a mask mount where they are centered on two pins. The position accuracy of the masks in the focal plane is anticipated to be better than ± 10 μm. A mechanism which locks the masks in their cabinets and releases only the one connected to the transport robot permits mask exchange in arbitrary orientation of the cryostat.
Infrared camera and spectrograph for the Subaru Telescope: performance improvement with the new Aladdin-III array
We report on the significantly improved performance of the Infrared Camera and Spectrograph (IRCS) for the Subaru Telescope. The IRCS consists of the camera side for imaging and grism spectroscopy and the spectrograph side for echelle spectroscopy. Due to the low sensitivity of the previous Aladdin-II engineering grade InSb infrared array on the camera side, the capability of imaging and grism spectroscopy was reduced. Thus, we replaced the array on the camera side into the new Aladdin-III array in August 2001. The newly installed Aladdin-III array has 1.9 times higher quantum efficiency (95%), 2/3 lower read-out noise (12e- with 16 non-destructive-readout at 27.5K of the array temperature) and better cosmetics than the old Aladdin-II array. We have also obtained grism spectra for a comparison of performances with the old and the new arrays. The spectra with the new array show about twice better signal-to-noise for each spectral element and almost no systematic noise. Currently we have two different types of arrays: Aladdin-II array on the spectrograph side and the science grade Aladdin-III array on the camera side. We will also present dark current, read-out noise, linearity curve and the other characteristics as a function of array temperatures to summarize the current performance of both arrays. We plan to upgrade the Aladdin-II array on the spectrograph side to a new Aladdin-III array in summer 2003.
Multiple integral field spectroscopy using image slicers
We present the results of a detailed technical study of the use of image slicers for multiple integral field spectroscopy at infrared wavelengths. Our solution uses independently controlled robotic arms to relay selected portions of the focal plane to fixed positions where they are dissected using a set of advanced image slicers. We discuss the technical requirements of this approach and describe a feasibility study to examine the risks and technical challenges.
Design and implementation of an atmospheric dispersion compensator/corrector for the Gemini multi-object spectrograph
Kei Szeto, Christopher L. Morbey, Christopher J. Mayer, et al.
The Gemini Multi-Object Spectrograph (GMOS) was delivered and commissioned at the Gemini North Observatory and it has been in regular science use since November 2001. While GMOS-North met all its reliability and performance requirements on flexure, image quality and throughput, the high velocity precision (2 km/sec) mode will not be implemented until the Atmospheric Dispersion Compensator/Corrector (ADC) is delivered and commissioned. The ADC optical design incorporating two bonded prism pairs and two corrector lenses is described along with its opto-mechanical and software control design considerations as related to the overall system requirements including: image quality, error budget, optical mounting, opto-mechanical packaging, mechanism control, handling, deployment and telescope observational control considerations.
Mechanical design of the IRIS2 infrared imaging camera and spectrograph
We describe the mechanical, optomechanical and thermal design and development of the IRIS2, an infrared imager and spectrograph for operation at the Cassegrain focus of the Anglo Australian Telescope. IRIS2 is reconfigured by four encoded worm driven wheels which carry slits and slit masks, filters, cold stops, and grisms, and a pupil imager. A detector translator provides fine focus. The instrument is housed in a split, or dual, vacuum vessel. Helium cryo-coolers provide operational cooling, but to reduce turn around time during commissioning and maintenance a liquid nitrogen pre-cooling system has been implemented in the main vessel. The slit wheel is housed in a separate, smaller vessel, which may be thermally cycled when new slit masks are installed, while the rest of the instrument remains at operational temperature. The common plate between the vessels serves as the structural base on which the instrument is assembled. Matched trusses on opposite sides of the plate minimize the relative deflection between the slit wheel assembly and the spectrograph optics.
The ICE spectrograph for PEPSI at the LBT: preliminary optical design
We present a preliminary design study for a high-resolution echelle spectrograph (ICE) to be used with the spectropolarimeter PEPSI under development at the LBT. In order to meet the scientific requirements and take full advantage of the peculiarities of the LBT (i.e. the binocular nature and the adaptive optics capabilities), we have designed a fiber-fed bench mounted instrument for both high resolution (R ≈ 100,000; non-AO polarimetric and integral light modes) and ultra-high resolution (R ≈ 300,000; AO integral light mode). In both cases, 4 spectra per order (two for each primary mirror) shall be accomodated in a 2-dimensional cross dispersed echelle format. In order to obtain a resolution-slit product of ≈ 100,000 as required by the science case, we have considered two alternative designs, one with two R4 echelles in series and the other with a sigle R4 echelle and fiber slicing. A white-pupil design, VPH cross-dispersers and two cameras of different focal length for the AO and non-AO modes are adopted in both cases. It is concluded that the single-echelle fiber-slicer solution has to be preferred in terms of performances, complexity and cost. It can be implemented at the LBT in two phases, with the long-camera AO mode added in a second phase depending on the availability of funds and the time-scale for implementation of the AO system.
Multi-object high-resolution echellette spectroscopy with IMACS
Brian M. Sutin, Andrew McWilliam
By adding a prism-cross-dispersed echellette grating as an optional module to the Inamori Magellan Areal Camera and Spectrograph (IMACS), complete spectra from 3400 to 11000Å of 15 simultaneous objects may be achieved with a resolution of R = 21,000 for a projected 0.5-arcsec slit width and a 5.0-arcsec slit length. The additional cost of this module is on the order of $50,000. This echellette module (IMACS-E) is intended for studies of stellar abundances where the targets are sufficiently dense over the 15 arcmin IMACS field of view to take advantage of the multi-slit capability. Such applications include the study of Galactic bulge stars, stars in local group galaxies, stars in Galactic globular and open clusters, and the integrated light of extra-galactic globular cluster systems.
AutoFib2: small fibers
Stephen J. Goodsell, Maarten F. Blanken, Romano Corradi, et al.
In July 2001, AutoFib-2 (AF2), the prime focus robotic fiber positioner for the Isaac Newton Group's (ING) 4.2m William Hershel Telescope (WHT) had its new Small Fiber Module (SFM) successfully commissioned. The new SFM contains 150 science fibers and 10 fiducial bundles. Each science fiber has a diameter of 90 μm, which corresponds to 1.6 arcsec in the sky. The continuous science fibers are fed into the Nasmyth platform Wide Field Fiber Optic Spectrograph (WYFFOS). Each fiducial bundle, 450 μm in diameter, contains 10,000 coherent fibers providing a rough imaging capability over an 8 arcsec round field. This paper looks at the reasons for developing this module, examines its mechanical design, describes its new science and fiducial fibers, looks at the fiber alignment techniques used, explains the new guiding system and briefly discusses changes in the AF2 control system. It continues to reveal the results of some fiber characterization experiments performed on sky and gives an example of a recent science run. The paper concludes with a section that lists planned AF2 enhancements.
Wavelength selection in OSIRIS
The Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) is an imaging system and a low-resolution long-slit and multi-object spectrograph for the 10.4m Spaninsh telescope GTC. OSIRIS spectral range (from 365 up to 1000 nm) and observing modes require a wide set of elements in order to provide imaging and spectroscopic capatibilities. Two tunable filters covering the full OSIRIS spectral range allow narrow band imaging with resolutions from R=300 to 1000. Twelve grisms provide spectral resolutions from R=250 through R=2500. In this contribution the design and characteristics of the tunable filters and grisms selected for OSIRIS are presented.
Comparison of open- vs. closed-loop flexure compensation systems for two Keck optical imaging spectrographs: ESI and DEIMOS
Two recent Keck optical imaging spectrographs have been designed with active flexure compensation systems (FCS). These two instruments utilize different methods for implementing flexure compensation. The Echellette Spectrograph and Imager (ESI), commissioned at the Cassegrain focus of the Keck II Telescope in late 1999, employs an open-loop control strategy. It utilizes a mathematical model of gravitationally-induced flexure to periodically compute flexure corrections as a function of telescope position. Those corrections are then automatically applied to a tip/tilt collimator to stabilize the image on the detector. The DEep Imaging Multi-Object Spectrograph (DEIMOS), commissioned at the Nasmyth focus of Keck II in June 2002, implements a closed-loop control strategy. It utilizes a set of fiber-fed FCS light sources at the ends of the slitmask to produce a corresponding set of spots on a pair of FCS CCD detectors located on either side of the science CCD mosaic. During science exposures, the FCS detectors are read out several times per minute to measure any translational motion of the FCS spot images. Correction signals derived from these FCS images are used to drive active optical mechanisms which steer the spots back to their nominal positions, thus stabilizing the FCS spot images as well as those on the science mosaic. We compare the design, calibration, and operation of these two systems on the telescope. Long-term performance results will be provided for the ESI FCS, and preliminary results will be provided for the DEIMOS FCS.
Fan Mountain Observatory bench spectrograph
Jeffrey D. Crane, Steven Majewski, Michael F. Skrutskie, et al.
The Bench Spectrograph at the University of Virginia's Fan Mountain Observatory is being built for use on the facility's primary research telescope, the 1-meter astrometric reflector. The spectrograph is designed for initial use as a dedicated instrument to collect moderate-resolution (10 km/s-1) spectra of candidate K giant stars for the Grid Giant Star Survey (GGSS), which is a program to identify stars for the Astrometric Grid of NASA's Space Interferometry Mission (SIM). The spectrograph is a single-object, fiber-fed design built with off-the-shelf optics at modest cost. The primary optics are transmissive, and a 1200 line/mm reflectance grating is used to provide a resolving power of R ~ 2000 at λ ~ 500 nm. Because the GGSS candidate sample is extensive, bright (V < 13), and uniformly distributed over the sky, a fiber-fed design was selected to provide maximal spectral stability and uniformity (to obtain high quality spectra, suitable for luminosity classification, abundance analysis, and radial velocity measurement) while optimizing observing efficiency. Although the primary wavelength region of interest for this application is 480-680 nm, the spectrograph will be useful throughout the optical spectrum. However, the combination of modest telescope aperture and characteristically low throughput will practically limit the spectrograph's usefulness to medium resolutions for stars brighter than about V~14.
Design of an f/1 camera for the HET low-resolution spectrograph IR extension
We present the optical design of the f/1 camera for the Hobby-Eberly Telescope Low Resolution Spectrograph Infrared Extension (LRS-J). This instrument extends the coverage of the LRS to 1300 nm by adding a fast cryogenic camera and volume holographic grisms (VPHG) to the LRS. This approach enables new science without the expense of building a complete new instrument. The camera is a catadioptric Maksutov type design, based on that of the optical LRS, that uses a HAWAII-1 1024x1024 detector. The design succeeds in imaging virtually all the light into one pixel over the HET field of view (FOV) and the wavelength range 900-1300 nm. We discuss the challenges of designing and manufacturing a fast camera for cryogenic use, and give details of the tolerance analysis.
The Eucalyptus spectrograph
Antonio Cesar de Oliveira, Beatriz Barbuy, Rodrigo Prates Campos, et al.
As part of the Brazilian contribution to the 4.2 m SOAR telescope project we are building the Integral Field Unit spectrograph, "SIFUS." With the aim of testing the performance of optical fibers with 50 microns core size on IFUs, we constructed a prototype of the IFU and a spectrograph that were installed at the 1.6 m telescope of the Observatorio do Pico dos Dias (OPD), managed by Laboratorio Nacional de Astrofisica (LNA) in Brazil. The IFU has 512 fibers coupled to a LIMO microlens array (16 x 32) covering a 15" x 30" field on the sky. The spectrograph is a medium resolution instrument, operating in a quasi-Littrow mode. It was based on the design of the SPIRAL spectrograph built by the Anglo-Australian Observatory. The name Eucalyptus was given following the name of the native Australian tree that adapted very well in Brazil and it was given in recognition to the collaboration with the colleagues of the Anglo-Australian Observatory. The instrument first light occurred in the first semester of 2001. The results confirmed the possibility of using the adopted fibers and construction techniques for the SIFUS. We present the features of the instrument, some examples of the scientific data obtained, and the status of the commissioning, calibration and automation plans. The efficiency of this IFU was determined to be 53% during telescope commissioning tests.
Spine development for the Echidna fiber positioner
Anna Marie Moore, Peter R. Gillingham, Jason S. Griesbach, et al.
The Echidna multi-object fiber positioner is part of the Fiber Multi-Object Spectrograph (FMOS) project for the prime focus of the Subaru telescope. Given the physical size of the focal plane and the required number of fibers (400), a positioning system based on the Anglo-Australian Observatory's 2dF instrument, that incorporates the placement of magnetic buttons by a single X/Y/Z robot, was considered impractical. Instead, a solution has been developed in which each fiber is mounted on a tilting spine that allows the fiber to be positioned anywhere in a circle of radius 7 mm. Each of the 400 fibers therefore has a fixed "patrol" area in the field of view, with a significant overlap between neighboring spines. A description of a single Echidna spine is presented. Each spine is driven by a quadrant tube piezoelectric actuator (QTP) that, by a ratcheting mechanism, is able to position the fiber to within 10 μm of any coordinate in the corresponding patrol area. Results of positioning tests for eight of the twenty prototype spines reveal better than specification performance, as well as a durability far in excess of the specified lifetime of the instrument.
Gemini-north multi-object spectrograph optical performance
Richard G. Murowinski, Jeremy R. Allington-Smith, David Crampton, et al.
The Gemini Multiobject Spectrographs (GMOS) were designed to take advantage of the exquisite image quality expected of the Gemini telescopes. To achieve this, two of the many requirements placed on the optical system was that it not degrade the best image quality expected of the telescope by more than 10% while delivering a throughput of about 80% over the entire 0.4-1 μm waveband. In this paper, key components of the design and execution of this optical system are discussed and test results are presented demonstrating that it meets these requirements on Gemini today. Among other characteristics, we look at the image quality performance as a function of colour and field angle, the measured throughput, and the focalplane flatness on the detectors.
Mechanical design of ELMER instrument for GTC telescope
Bernardo Ronquillo, Miguel Angel Vega, Rafael Garcia, et al.
ELMER is an optical instrument for the GTC designed to observe between 370 and 1000 nm. The observing modes for the instrument at Day One shall be: imaging, long slit spectroscopy, slit-less multi-object spectroscopy, fast photometry, fast short-slit spectroscopy and mask multi-object spectroscopy. It will be installed at the Nasmyth-B focal station at Day One, but it has also been designed to operate at the Folded Cassegrain focal station. The physical configuration of the instrument consists of a front section where the focal plane components are mounted (cover masks and slits) and a rear section with the rest of the components (field lens, folder mirrors, collimator, shutter, filters, prisms, grisms, camera and cryostat). Both sections are connected through a hexapod type structure. An accurate behavior model of the instrument has been developed to optimize the design of the structural parts. The geometry of the hexapod configuration has been adjusted to reduce the ratio between the lateral deflection of the rear section and its rotation in order to minimize the image motion due to the deflections of the instrument. Special effort has been devoted to the design of the drives of the four wheels, each one driven by a preloaded worm gear.
Prime focus imaging spectrograph for the Southern African Large Telescope: optical design
Eric B. Burgh, Kenneth H. Nordsieck, Henry A. Kobulnicky, et al.
The University of Wisconsin - Madison, together with Rutgers University and the South African Astronomical Observatory, is designing and building an imaging spectrograph for the Prime Focus Instrument Package of the Southern African Large Telescope (SALT). The Prime Focus Imaging Spectrograph (PFIS) will be a versatile instrument specializing in very high throughput, low and medium resolution (R=500-12,500) imaging spectroscopy, using volume phase holographic (VPH) gratings and a double etalon Fabry-Perot interferometer, and spectropolarimetry from 320 to 900 nm. The optical design includes all transmissive optics for high efficiency and compactness. To maintain throughput in the ultraviolet, only fused silica, CaF2 and NaCl are used. As NaCl is very hygroscopic, the design uses NaCl as the inner element in sealed triplets only. For the highest possible first-order spectral resolution, the collimated beam size is 150 mm - the maximum for practical Fabry-Perot etalons. The F/2.2 camera can be articulated to tune the efficiency of the VPH gratings; a complement of six gratings (5 VPH and 1 standard transmission grating) has been designed to fill the resolution-wavelength space available to the instrument. Linear, circular, and all-stokes spectropolarimetry will be performed through the use of Pancharatnam superachromatic waveplates and a Wollaston beamsplitter.
FaNTOmM: Fabry Perot of new technology for the Observatoire du mont Megantic
We present a third generation instrument using a photon counting camera (IPCS) based on an GaAs photo cathode that can achieve quantum efficiency up to 28%, comparable to a thick CCD, but without readout noise. This system is 10 times more sensitive at the Hα wavelength than previous Fabry Perot system used at the Observatoire du mont Mégantic. In terms of S/N ratio, the system outperforms CCD for extremely faint fluxes, included AR coated low noise thin CCDs. This system offers up to 1k x 1k pixels which is the largest monolithic IPCS. An original cooling system is used for camera based on a Ranque-Hilsh vortex tube. The real-time centering is done by a scalable DSP board. FaNTOmM is the association of a focal reducer (PANORAMIX: the 1.6m mont Megantic OmM telescope focal reducer), a Fabry Perot etalon and an IPCS. Preliminary results obtained with the 1.6m mont Megantic telescope are presented.
Thermal effects and thermal compensation in the OSIRIS camera
J. Jesus Gonzalez, Carlos Tejada, Alejandro Farah, et al.
Tight stability requirements for the imager/spectrograph OSIRIS (a Day One optical instrument for the GTC telescope) demand a careful treatment of thermal effects within the OSIRIS camera. Mostly due to the thermal response of refraction indices of its glasses (and not so much to curvature, spacing or thickness variations of the lenses), the camera optics alone degrades beyond requirements the image quality and plate scale under the expected ambient temperature variations (about 1.8 °C/hour). Thermal effects and thermal compensator studies of the OSIRIS camera are first summarized, before discussing how the motion (of a few microns per °C) of the 3rd camera doublet, as a sole compensator, practically eliminates thermal influences on both image quality and plate scale. A concept for the passive implementation of the compensator is also discussed.
HERCULES: a high-resolution spectrograph for small- to medium-sized telescopes
Stuart I. Barnes, John B. Hearnshaw, Graeme Kershaw, et al.
The High Efficiency and Resolution Canterbury University Large Echelle Spectrograph (HERCULES) is a fibre-fed echelle spectrograph that has been in operation at the Mount John University Observatory for just over one year. HERCULES is used in conjunction with the 1-m McLellan telescope, and can capture the spectrum from 380 nm to 880 nm on a single 50-mm square CCD. Resolving powers of up to 70000 are possible when using 50-μm fibres, and a resolving power of 35000 is possible with a 100-μm fibre. Wavelength calibration is done using sequential exposures of a thorium-argon emission lamp. The spectrograph is designed to achieve high efficiency when the seeing is well matched to the image scale on the fibre input (up to 20% in 1 arcsec seeing), and high stability is achieved by having the spectrograph installed inside a vacuum tank in a thermally isolated environment. Initial indications are that radial velocities with a precision of ≤ 10 ms-1 are routinely possible in the short-term.
Integral-field spectroscopy at the resolution limit of large telescopes: the science program of OSIRIS at Keck
OSIRIS (OH-Suppressing InfraRed Integral-field Spectrograph) is a new facility instrument for the Keck Observatory. Starting in 2004, it will provide the capability of performing three-dimensional spectroscopy in the near-infrared z, J, H, and K bands at the resolution limit of the Keck II telescope, which is equipped with adaptive optics and a laser guide star. The innovative capabilities of OSIRIS will enable many new observing projects. Galaxies in the early Universe will be among the most interesting targets for OSIRIS, which will perform detailed studies of their stellar content and dynamical properties. In more exotic objects, such as quasars, radio galaxies, and more nearby active galactic nuclei, OSIRIS can elucidate the relation of the central black hole to the properties of the host galaxy, and the mechanism by which gas is fed into the central engine. In the center of our own Galaxy, it will be possible to search for signatures of interaction between the massive black hole and stars in its immediate vicinity. Closer to home, OSIRIS will perform spectroscopic observations of young stars and their environment, and of brown dwarfs. Imaging spectroscopy of the giant planets, their moons, and asteroids will shed new light on meteorology, mineralogy, and volcanism in the Solar System. OSIRIS observations of Kuiper Belt objects will provide sufficient sensitivity to establish their surface composition, which will contribute substantially to our understanding of the history of the Solar System.
Design and performance of a versatile Penn State near-infrared imager and spectrograph
A versatile near IR instrument called Penn State near IR Imager and Spectrograph (PIRIS) with a 256 x 256 PICNIC IR array has been developed at Penn State and saw its first light at the Mt. Wilson 100 inch in October 2001. The optical design consists of five optical subsystems including (1) the slit aperture wheel, (2) an achromat collimator optic, (3) a grism/filter and pupil assembly, (4) a pupil imaging optic, and (5) achromat camera optics. This instrument has imaging, spectroscopy and coronagraph modes. It is being updated to have an integral field 3-D imaging spectroscopy mode and a very high IR spectroscopy mode (R ~ 150,000) with an anamorphic silicon immersion grating in 2003. The instrument is designed to take full advantage of high Strehl ratio images delivered by high order adaptive optics systems. Its imaging mode has f/37 and f/51 optics to allow diffraction-limited imaging in H and K bands, respectively. Its spectroscopy mode has R = 20, 180, 400, 2000, and 5000. The lowest resolution is obtained with a non-deviation prism. The medium resolution spectroscopy mode is conducted with three commercial fused-silica grisms. They can be either used in long slit spectroscopy mode with a blocking filter or used as a cross-disperser for a high resolution silicon grism. High resolution spectroscopy is done with silicon grisms and cross-disperser grisms, which are designed to work on high orders (~ 80) to completely cover H and K bands for R = 5000 separately, or simultaneously cover H and K bands for R = 2000. Coronagraphy is done by inserting an apodizing mask, held in the slit aperture wheel, in the focal plane and a Lyot stop (pupil mask) at a reimaged pupil inside the dewar. Image contrast can be enhanced by using different combinations of the apodizing mask and pupil mask. Several of Gaussian pupil masks have also been installed in the pupil wheel for high contrast imaging. We have successfully detected two substellar companions during our first light at Mt. Wilson 100 inch telescope. We were also able to evaluate our cononagraphy and gaussion pupil mask modes, which demonstrate 10-3 - 10-4 contrast 1 arcsec region around a bright point source. A hybrid coronagraph mode, a combination of an apodizing focal plane mask with a Gaussian shaped pupil mask, has been tested and produces 10-5 - 10-6 deep contrast as close as 4 λ/D at 2.2 μm in the lab. Low resolution spectroscopy modes including a vision prism (R = 20) and three fused silicon grisms (R = 200 - 400) have been tested in the lab. The spectroscopy results are reported here.
Design of a slit mechanism for OSIRIS
Carmelo Militello, Santiago Correa, Jaime Perez, et al.
OSIRIS (Optical System for Imaging and low/intermediate-Resolution Integrated Spectroscopy) is an instrument designed to obtain images and low resolution spectra of astronomical objects in the optical domain (from 365 through 1000nm). It will be installed on Day One in the Nasmyth focus of the 10-meter Spanish GTC Telescope, although it shall be possible to install it in the Cassegrain focus as well. It is expected to be in operation at the end of 2003. The Slit Unit is an automated slit mask loader based in cam followers technology, being designed at the IAC for the OSIRIS Spectrograph. It provides a store with space for as many as 13 multislits mask and long slit mask for an unvignetted field of view of 8.53'x8.67', available at the same time for observing purposes. A two-degrees-of-freedom mechanism allows to select one of the masks, to remove it from the cassette and to position it in the focal plane with the required repeatability. The complete design of the mechanism is presented, including an analysis of the predicted performances and a 3-D model used to check the geometry and mass properties.
IR Spectrogaphs II
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EMIR: the GTC NIR multi-object imager spectrograph
In this contribution we review the overall features of EMIR, the NIR multiobject spectrograph of the GTC. EMIR is at present in the middle of the PD phase and will be one of the first common user instruments for the GTC, the 10 meter telescope under construction by GRANTECAN at the Roque de los Muchachos Observatory (Canary Islands, Spain). EMIR is being built by a Consortium of Spanish, French and British institutes led by the IAC. EMIR is designed to realize one of the central goals of 10m class telescopes, allowing observers to obtain spectra for large numbers of faint sources in an time-efficient manner. EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2.5 μm. The present status of development, expected performances and schedule are described and discussed. This project is funded by GRANTECAN and the Plan Nacional de Astronomía y Astrofísica (National Plan for Astronomy and Astrophysics, Spain).
SINFONI: integral field spectroscopy at 50-milli-arcsecond resolution with the ESO VLT
Frank Eisenhauer, Roberto Abuter, Klaus Bickert, et al.
SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.
KMOS: an infrared multi-integral field spectrograph for the VLT
Ray M. Sharples, Ralf Bender, Reiner Hofmann, et al.
We describe a proposed 2nd generation instrument (KMOS) for the ESO VLT which will deliver a unique multiple integral field capability in the near-infrared (1-2.5 μm). The science drivers for such an instrument are presented and linked to the functional specification. The overall instrument concept is discussed in the context of two proposed solutions for delivering a deployable integral field capability. Detailed discussions of these two approaches, and ongoing prototype studies, are described in separate papers.
TEXES: a sensitive and versatile spectrograph for mid-infrared astronomy
TEXES, the Texas Echelon Cross Echelle Spectrograph, is a versatile mid-infrared (5-25 μm) spectrograph that can be used in several operating modes: high resolution cross-dispersed, with a resolving power of R = 50-100,000; medium resolution long-slit, with R~15,000; low resolution long-slit, with R~3000; source acquisition imaging; and pupil imaging. The design of TEXES is unique in several respects. The primary disperser is a variation on an echelon, a steeply and coarsely blazed (R10 with 0.3 inch groove spacing), 36 inch long, diamond-machined aluminum grating. The cross disperser is an R4 echelle used in low order at R2, with the grooves acting as corner reflectors. Cold mechanisms allow the echelon to be bypassed to use the cross disperser in long-slit mode. A first-order grating can be inserted in front of the echelle for lower resolution. In addition, the low resolution grating can be turned face-on to act as a mirror allowing source-acquisition imaging and pupil viewing. TEXES has been used for 8 nights on the McDonald Observatory 2.7m and 45 nights on the NASA IRTF 3m telescopes over the last 2 1/2 years. Sources observed include planets and planetary satellites, stellar atmospheres, circumstellar outflows and disks, and molecular clouds and HII regions in the Milky Way and external galaxies.
Gemini near-infrared integral field spectrograph (NIFS)
NIFS is a near-infrared integral field spectrograph designed for near diffraction-limited imaging spectroscopy with the ALTAIR facility adaptive optics system on Gemini North. NIFS is currently under construction at the Research School of Astronomy and Astrophysics of the Australian National University. Commissioning is planned for 2003. NIFS uses a reflective concentric integral field unit to reformat its 3.0"x3.0" field-of-view into 29 slitlets each 0.1" wide with 0.04" sampling along each slitlet. The NIFS spectrograph has a resolving power of ~ 5300, which is large enough to significantly separate terrestrial airglow emission lines and resolve velocity structure in galaxies. The output format is matched to a 2048x2048 pixel Rockwell HAWAII-2 detector. The detector is read out through a SDSU-2 detector controller connected via a VME interface to the Gemini Data Handling System. NIFS is a fast-tracked instrument that reuses many of the designs of the Gemini Near-InfraRed Imager (NIRI); the cryostat, On-Instrument Wave Front Sensor, control system, and control software are largely duplicates.
CRIRES: a high-resolution infrared spectrograph for the ESO VLT
Alan F. M. Moorwood, Peter Biereichel, Joar Brynnel, et al.
CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power of 105 between 1 and 5 μm at a Nasmyth focus of one of the 8m VLT telescopes. A curvature sensing adaptive optics sytem feed is used to minimize slit losses and a 4096x512 pixel mosaic of Aladdin arrays is being developed to maximixe the free spectral range covered in each order. Insertion of gas cells to measure high precision radial velocities is foreseen and the possibility of combining a Fresnel rhomb with a Wollaston prism for magnetic Doppler imaging is under study. Installation at the VLT is scheduled during the second half of 2004. Here we briefly recall the major design features of CRIRES and describe its current development status.
OSIRIS: an infrared integral field spectrograph for the Keck adaptive optics system
We present the design for a recently approved instrument for the Keck Telescope. Called OSIRIS, it was inspired by the optical spectrograph TIGER of R. Bacon et al. and will utilize an infrared transmissive lenslet array to sample a rectangular field of view at close to the Keck diffraction limit. By packing the spectra very closely together (2 pixel rows per spectrum) and using the Rockwell Hawaii-2 detector (wavelengths between 1 and 2.5 microns), we will achieve a relatively large field of view (up to 6."4) while maintaining full broad-band spectral coverage at a resolution of 3900. Due to the extremely low backgrounds between night sky lines and at AO spatial samplings, the instrument will reach point source sensitivities several times fainter than any existing infrared spectrograph. We are also coupling a separate infrared AO camera dubbed SHARC to work as an acquisition camera and to monitor the point spread function's behavior during long spectroscopic exposures. Among the challenges of the instrument are: a fully cryogenic design, four spatial resolutions from 0."02 to 0."10, large aluminum optics for the spectrography, extremely repeatable spectral formats and a sophisticated data reduction pipeline.
Performance of the FLAMINGOS near-IR multi-object spectrometer and imager and plans for FLAMINGOS-2: a fully cryogenic near-IR MOS for Gemini South
Richard Elston, Steven N. Raines, Kevin T. Hanna, et al.
We report on the performance of FLAMINGOS, the world's first fully cryogenic near-IR multi-object spectrometer. FLAMINGOS has a fast all refractive optical system, which can be used at telescopes slower than f/7.5. This makes FLAMINGOS a very efficient wide-field imager when used on fast small aperture telescopes and a high AW spectrometer using laser machined aperture masks for MOS spectroscopy. FLAMINGOS uses a 2048x2048 HgCdTe HAWAII-2 array by the Rockwell Science Center. The array is readout through 32 amplifiers, which results in low overheads for observations. We describe both the operating characteristics of the HAWAII-2 array and of the array controller and data acquisition system. FLAMINGOS has been in operation for about 1.5 years and is now in routine use on four telescopes: The Kitt Peak 4-m and 2.1-m, The 6.5-m MMT and the 8-m Gemini South Telescope. We will describe the operating characteristics of FLAMINGOS on each of these telescopes that deliver fields-of-view from 21x21 arcminutes to 2.7x2.7 arcminutes and pixels from 0.6 arcseconds to 0.08 arcseconds. While providing a large AW product for fast telescopes (i.e. f/8), FLAMINGOS becomes progressively less efficient on slower telescopes. Since nearly all large telescopes have fairly slow optical systems (f/12 or slower) the combination of large aperture and slow optical systems makes FLAMINGOS ill suited for optimal performance on current large aperture telescopes. Thus, we are beginning construction of FLAMINGOS-2, which will be optimized for performance on the f/16 Gemini South 8-m telescope. Similar to FLAMINGOS, FLAMINGOS-2 will be fully refractive using grisms, laser machined aperture masks and a 2048x2048 HgCdTe HAWAII-2 array. FLAMINGOS-2 will provide a 6.1 arcminute field-of-view with 0.18 arcsecond pixels. FLAMINGOS-2 will also be designed to except an f/32 beam from the Gemini South MCAO system.
MOIRCS: muti-object infrared camera and spectrograph for the Subaru Telescope
MOIRCS (Multi-Object InfraRed Camera and Spectrograph) is one of the second generation instruments for the Subaru Telescope. This instrument is under construction by the National Astronomical Observatory of Japan and Tohoku University. It has imaging and multi-object spectroscopy (MOS) capabilities in the wavelength range from 0.85 μm to 2.5 μm with 4' x 7' F.O.V. The focal plane is imaged onto two 2048 x 2048 pixel HAWAII-2 HgCdTe arrays with a pixel scale of 0."12 pixel-1 through two independent optical trains. The optical design is optimized to maximize K band performance. Unique design of MOIRCS allows multi-object spectroscopy out to K band with cooled multi-slit masks. Twenty-four masks are stored in a mask dewar and are exchanged in the cryogenic environment. The mask dewar has its own vacuum pump and cryogenic cooler, and the masks can be assessed without breaking the vacuum of the main dewar. The two-channel optics and arrays are mounted back-to-back of a single optical bench plate. A PC-Linux based infrared array control system has been prepared to operate HAWAII-2. The first light of MOIRCS is planned in the spring of 2003.
Optical Spectrograph I
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Prime Focus Imaging Spectrograph for the Southern African Large Telescope: operational modes
Henry A. Kobulnicky, Kenneth H. Nordsieck, Eric B. Burgh, et al.
The Prime Focus Imaging Spectrograph (PFIS) will be the workhorse first-light instrument on the Southern African Large Telescope (SALT). Scheduled for commissioning in late 2004, PFIS is a versatile high-throughput imaging spectrograph with a complement of 5 volume-phase holographic gratings for spectroscopic programs from 3200Å to 9000Å at resolutions of R=1500 to R=6000. A magazine of 6 longslits and 30 custom laser-milled slitmasks enables single- or multi-object spectroscopy over an 8 arcminute diameter field. With the gratings stowed, a dual-etalon Fabry-Perot subsystem enables imaging spectroscopy at R=500, R=3000, and R=12,500. The polarization subsystem, consisting of a polarizing beam-splitter used in conjunction with half- and quarter-wave plates, allow linear or circular polarimetric measurements in ANY of the spectroscopic modes. Three mosaiced rapid-readout frame-transfer CCDs provide the capability for time-resolved sampling at rates in excess of 10 Hz. Combinations of these subsystems permit novel observing modes for specialized scientific programs. Examples include high-time resolution multi-object spectral polarizmetry of accreting compact objects, and Fabry-Perot polarimetry or imaging spectral polarimetry of nebulae and stellar clusters. The demands of queue-scheduled observing on a fixed-altitude telescope require that the instrument be capable of rapid reconfiguration between modes.
IR Spectrographs I/Cameras I
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The Fiber Multi-Object Spectrograph (FMOS) project: the Anglo-Australian Observatory role
Peter R. Gillingham, Anna Marie Moore, Masayuki Akiyama, et al.
The Fiber Multi-Object Spectrograph (FMOS) project is an Australia-Japan-UK collaboration to design and build a novel 400 fiber positioner feeding two near infrared spectrographs from the prime focus of the Subaru telescope. The project comprises several parts. Those under design and construction at the Anglo-Australian Observatory (AAO) are the piezoelectric actuator driven fiber positioner (Echidna), a wide field (30 arcmin) corrector and a focal plane imager (FPI) used for controlling the positioner and for field acquisition. This paper presents an overview of the AAO share of the FMOS project. It describes the technical infrastructure required to extend the single Echidna "spine" design to a fully functioning multi-fiber instrument, capable of complete field reconfiguration in less than ten minutes. The modular Echidna system is introduced, wherein the field of view is populated by 12 identical rectangular modules, each positioning 40 science fibers and 2 guide fiber bundles. This arrangement allows maintenance by exchanging modules and minimizes the difficulties of construction. The associated electronics hardware, in itself a significant challenge, includes a 23 layer PCB board, able to supply current to each piezoelectric element in the module. The FPI is a dual purpose imaging system translating in two coordinates and is located beneath the assembled modules. The FPI measures the spine positions as well as acquiring sky images for instrument calibration and for field acquisition. An overview of the software is included.
Optical Spectrograph I
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Gemini-North multi-object spectrograph integration, test and commissioning
Isobel Hook, Jeremy R. Allington-Smith, Steven M. Beard, et al.
The first of two Gemini Multi Object Spectrographs (GMOS) has recently begun operation at the Gemini-North 8m telescope. In this presentation we give an overview of the instrument and describe the overall performance of GMOS-North both in the laboratory during integration, and at the telescope during commissioning. We describe the development process which led to meeting the demanding reliability and performance requirements on flexure, throughput and image quality. We then show examples of GMOS data and performance on the telescope in its imaging, long-slit and MOS modes. We also briefly highlight novel features in GMOS that are described in more detail in separate presentations, particularly the flexure compensation system and the on-instrument wavefront sensor. Finally we give an update of the current status of GMOS on Gemini-North and future plans.
The DEIMOS spectrograph for the Keck 2 Telescope: Integration and testing
The DEIMOS spectrograph is a multi-object spectrograph being built for Keck II. DEIMOS was delivered in February 2002, became operational in May, and is now about three-quarters of the way through its commissioning period. This paper describes the major problems encountered in completing the spectrograph, with particular emphasis on optical quality and image motion. The strategies developed to deal with these problems are described. Overall, commissioning is going well, and it appears that DEIMOS will meet all of its major performance goals.
Installation and first results of FLAMES, the VLT multifiber facility
Luca Pasquini, Jaime Alonso, Gerardo Avila, et al.
FLAMES is the VLT Fibre Facility, installed and being commissioned at the Nasmyth A of UT2 (Kueyen Telescope). FLAMES has been built and assembled at the VLT telescope in about 4 years through an international collaboration between 10 institutes in 6 countries and 3 continents. It had first light with the fibre link to the red arm of UVES on April 1, and with the GIRAFFE spectrograph on July 3. We have not yet enough data to compare the observed vs. expected astronomical performances, although these first data are encouraging in many respects. We aim at proceeding soon with the remaining tests
Commissioning and performances of the VLT-VIMOS
Oliver LeFevre, Michel Saisse, Dario Mancini, et al.
The Visible Multi-Object Spectrograph VIMOS is a wide field survey instrument in the process of being commissioned for operations at the ESO-VLT. During the first commissioning period, the instrument has confirmed its excellent performances in its three basic modes of operation: direct imaging, multi-slit spectroscopy, and integral field spectroscopy. VIMOS provides the largest imaging field at the VLT with 224 arcmin2. It offers an unprecedented multiplex gain in multi-slit spectroscopy, with on order 800 slits which can be observed simultaneously. The integral field unit has a field up to 54x54 arcsec2, with 6400 spectra recorded at once. The overall efficiency of VIMOS combined to the Melipal unit #3 is confirmed to be as computed on the basis of the measured transmission of optical elements. Image quality is confirmed to be excellent, providing images limited by natural seeing in most conditions. High quality slit masks cut by the laser machine coupled to excellent geometric mask to CCD mapping lead to multi-slit spectra of excellent quality. VIMOS is expected to be offered to the ESO community for reguglar observations in early 2003.
MIKE: a double-echelle spectrograph for the Magellan Telescopes at Las Campanas Observatory
Rebecca Bernstein, Stephen A. Shectman, Steven M. Gunnels, et al.
The Magellan Inamori Kyocera Echelle (MIKE) is a double echelle spectrograph designed for use at the Magellan Telescopes at Las Campanas Observatory in Chile. It is currently in the final stages of construction and is scheduled for commissioning in the last quarter of 2002. In standard observing mode, the blue (320-480 nm) and red (440-1000 nm) channels are used simultaneously to obtain spectra over the full wavelength range with only a few gaps in wavelength coverage at the reddest orders. Both channels contain a three-group set of all-spherical, standard optical glass and calcium fluoride lenses which function as both camera and collimator in a double pass configuration. A single, standard echelle grating is used on each side and is illuminated close to true Littrow. Prism cross-dispersers are also used double-pass, and provide a minimum separation between orders of 6 arcsec. Spectral resolution is 19,000 and 25,000 on the red and blue sides, respectively, with a 1 arcsec slit. Typical rms image diameter is less than 0.2 arcsec, so that resolution increases linearly with decreasing slit width. The standard observing mode will use a slit up to 5" long, however a fiber-fed mode will also be available using blocking filters to select the desired orders for up to 256 objects at a time. In this paper, we describe the optical and mechanical design of the instrument.
Status of Elmer: an instrument for the GTC 10-m telescope (Gran Telescopio CANARIAS)
Elmer is an imager and spectrograph in the visible wavelength range for the Gran Telescopio CANARIAS, GTC. Elmer is being managed directly by the GTC Project Office, who has done the whole Preliminary Design and large part of the Detailed Design. This instrument shall operate at the telescope on Day One, as a back up in case of delays of the major instruments, guaranteeing the scientific return of the GTC. A brief presentation of the instrument is here given. The expected scientific performance of the instrument is summarized. Finally, the general description of the management strategy and project parameters are described.
Optical Spectrograph II
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IMACS: the multi-object spectrograph and imager for Magellan: a status report
Bruce C. Bigelow, Alan M. Dressler
The Inamori Magellan Areal Camera and Spectrograph (IMACS) will soon be one of the three first-generation instruments for the Magellan 6.5m telescopes. This instrument drove the specification and design of the f/11 Gregorian focus on Magellan, which it uses to feed an all-spherical, refracting wide-field collimator with a 30 arcmin field of view. Two Epps cameras are used to re-image the field of view for imaging and spectroscopy. The aspheric, f/2 ("short") camera images a field of 27 x 27 arcmin at 0.2 arcsec/pixel, and produces 0.32 arcsec images averaged over all field positions across the 0.39 -1.05 micron bandpass. The all-spherical f/4 ("long") camera images a field 15 x 15 arcmin at 0.11 arcsec/pixel, and produces 0.16 arcsec images averaged over all field positions across the 0.365 - 1.0 micron bandpass. This paper describes the final specifications for the multiple spectrographic and imaging modes, and provides a status report on the current state of the instrument project.
OSIRIS tunable imager and spectrograph for the GTC-instrument status
Jordi Cepa, Marta Aguiar-Gonzalez, Jonathan Bland-Hawthorn, et al.
OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC to be installed in the Observatorio del Roque de Los Muchachos (La Palma, Spain). This instrument, operational in mid-2004, covers from 360 up to 1000 nm. OSIRIS observing modes include direct imaging with tunable and conventional filters, long slit and multiple object spectroscopy and fast spectrophotometry. The OSIRIS wide field of view, high efficiency and the new observing modes (tunable imaging and fast spectrophotometry) for 8-10m class telescopes will provide GTC with a powerful tool for their scientific exploitation. The present paper provides an updated overview of the instrument development, of some of the scientific projects that will be tackled with OSIRIS and of the general requirements driving the optical and mechanical design.
Gemini-North multi-object spectrograph: integral field unit
Graham J. Murray, Jeremy R. Allington-Smith, Robert Content, et al.
The Gemini-North Multiobject Spectrograph (GMOS) includes a powerful capability for integral field spectroscopy - the first to be installed and used on an 8-10m telescope. GMOS is switched to this mode by the remote insertion of an integral field unit (IFU) into the focal plane in place of the masks used for multiobject spectroscopy. With 1500 lenslet-coupled fibres, it provides a total field of view exceeding 50 square arcseconds, including a separate field dedicated to background subtraction. We describe the design, construction and testing of the IFU and present performance results obtained during commissioning.
Wide-field optical spectrograph concept for a 30-m telescope
An optical design for a wide-field optical spectrograph has been developed as part of a point design study for a 30-meter telescope conducted by the AURA New Initiatives Office. The design discusses a feasible means to implement a 20 arc-minute field of view feeding spectrographs via fiber optics for low to moderately high resolution spectroscopy in the optical and near infrared spectral window. That concept is described in this paper.
The VIRMOS very wide integral field unit for the VLT: integration and performances
Christophe Bonneville, Eric Prieto, Oliver LeFevre, et al.
We present the integration and performances of the VLT-VIMOS Integral Field spectroscopy Unit. This unit allows to observe a very large 54x54 arcsec2 field on the side of the VIMOS instrument multi-object field in the range 0.37 - 1μm. This unit contains 6400 sets of micro-lenses - fibers - micro-lenses, producing the equivalent of a 72 arcmin x 0.67 arcsec slit projected on the sky. Two spatial resolutions (0.67 arcsec and 0.33 arcsec) are offered, coupled with the low and high spectral resolution of VIMOS. After reviewing the design philosophy, we are presenting the main steps and challenges encountered during integration. Calibration tests conducted in France and at the Paranal observatory as well as the data reduction software that has been developed for IFU are discussed. The first sky images of this very wide Integral Field Unit have been obtained in the early 2002 commissioning periods at VLT.
Poster Session B
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CPng: a high-sensitivity photon-counting camera
Eric Thiebaut, L. Abbe, Alain Blazit, et al.
CPng is a photon-counting camera currently under final development at Observatoire de Lyon, France and Observatoire de la Cote d Azur, France. Its goal is to provide quantum efficiency as high as possible at visible wavelengths up to 30-35 %under very low light level conditions and with a very short exposure time, approximately 4ms. Five CPng devices are under construction for astronomical and bio-medical imaging.
Back-and-forth spectroscopy: optimization of an optical nod-and-shuffle technique to reach fainter objects and increase the multiplex gain on multi-object spectrographs
Jean-Charles Cuillandre, Bernard Pierre Fort, Jean-Pierre Picat, et al.
Back on several on-sky tests using the Multi-Object Spectrography at the Canada-France-Hawaii Telescope, we present refinements of the faint objects optical spectroscopy technique we proposed in 1994 (initially names "Va-et-Vient" = "Back-and-Forth"), a nod-and-shuttle technique that preserves a sky dominated photon noise regime. We validated schemes that allow 100% of the total telescope time used to integrate the light from the scientific objects. We also investigated how to optimize the configuration of the charge sifting in order to use minimal space on the detector. For typical distant galaxy fields (profile dominated by seeing), we demonstrated an increase by a factor of approximately 2 of the multiplex gain and even higher for more compact sources. The technique proves perfectly apt at eliminating all the systemic errors that may cause the saturation of the signal-to-noise ratio: slit defects, CCD fringing, and flat-field residuals. This technique is also the most efficient and unique approach to use curved slits.