Proceedings Volume 4853

Innovative Telescopes and Instrumentation for Solar Astrophysics

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Proceedings Volume 4853

Innovative Telescopes and Instrumentation for Solar Astrophysics

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Volume Details

Date Published: 11 February 2003
Contents: 12 Sessions, 67 Papers, 0 Presentations
Conference: Astronomical Telescopes and Instrumentation 2002
Volume Number: 4853

Table of Contents

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Table of Contents

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  • Heliospheric Imaging
  • Poster Session
  • High Energy Observations
  • Radio
  • Poster Session
  • Balloon Missions
  • Poster Session
  • Space Missions and Instrumentation I
  • Poster Session
  • Polarimetry of the Solar Atmosphere I
  • Polarimetry of the Solar Atmosphere II
  • Ground Based Telescopes and Instruments I
  • Ground Based Telescopes and Instruments II
  • Poster Session
  • Ground Based Telescopes and Instruments II
  • Poster Session
  • Space Missions and Instrumentation II
  • Poster Session
  • Space Missions and Instrumentation II
  • Space Missions and Instrumentation III
  • Space Missions and Instrumentation II
  • Space Missions and Instrumentation III
  • Poster Session
  • Ground Based Telescopes and Instruments II
  • Poster Session
  • Polarimetry of the Solar Atmosphere I
Heliospheric Imaging
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The COR1 inner coronagraph for STEREO-SECCHI
William T. Thompson, Joseph M. Davila, Richard R. Fisher, et al.
The Solar Terrestrial Relations Observatory (STEREO) is a pair of identical satellites that will orbit the Sun so as to drift ahead of and behind Earth respectively, to give a stereo view of the Sun. STEREO is currently scheduled for launch in November 2005. One of the instrument packages that will be flown on each of the STEREO spacecrafts is the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI), which consists of an extreme ultraviolet imager, two coronagraphs, and two side-viewing heliospheric imagers to observe solar coronal mass ejections all the way from the Sun to Earth. We report here on the inner coronagraph, labeled COR1. COR1 is a classic Lyot internally occulting refractive coronagraph, adapted for the first time to be used in space. The field of view is from 1.3 to 4 solar radii. A linear polarizer is used to suppress scattered light, and to extract the polarized brightness signal from the solar corona. The optical scattering performance of the coronagraph was first modeled using both the ASAP and APART numerical modeling codes, and then tested at the Vacuum Tunnel Facility at the National Center for Atmospheric Research in Boulder, Colorado. In this report, we will focus on the COR1 optical design, the predicted optical performance, and the observed performance in the lab. We will also discuss the mechanical and thermal design, and the cleanliness requirements needed to achieve the optical performance.
Design and tests for the heliospheric imager of the STEREO mission
The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO spacecrafts to be launched in 2005. The two HI instruments will provide stereographic image pairs of solar coronal plasma and coronal mass ejections (CME) over a wide field of view (~90°), ranging from 13 to 330 R0. These observations compliment the 15 R0 field of view of the solar corona obtained by the other SECCHI instruments (2 coronagraphs and an EUV imager). The key challenge of the instrument design is the rejection of the solar disk light, with total straylight attenuation of the order of 10-13 to 10-15. A multi-vane diffractive baffle system has been theoretically optimized to achieve the lower requirement (10-13 for HI-1) and is combined with a secondary baffling system to reach the 10-15 rejection performance in the second camera system (HI-2). This paper presents the last updates of the SECCHI/HI design concept, with the expected performance. A verification program is currently in progress. The on-going stray-light verification tests are discussed. A set of tests has been conducted in air, and under vacuum. The results are presented and compared with the expected theoretical data.
Time-dependent tomography of heliospheric features using the three-dimensional reconstruction techniques developed for the solar mass ejection imager (SMEI)
Precise photometric images of the heliosphere are expected from the Air Force/NASA Solar Mass Ejection Imager (SMEI) now scheduled for launch in February 2003, and the all-sky cameras proposed for other NASA missions. To optimize the information available from these instruments, we are developing tomographic techniques for analyzing remote sensing observations of heliospheric density as observed in Thomson scattering (e.g. using the Helios photometer data) for eventual use with SMEI. We have refined the tomography program to enable us to analyze time-dependent phenomena, such as the evolution of corotating heliospheric structures and more discrete events such as coronal mass ejections. Both types of phenomena are discerned in our data, and are reconstructed in three dimensions. We use our tomography technique to study the interaction of these phenomena as they move outward from the Sun for several events that have been studied by multiple spacecraft in situ observations and other techniques.
Poster Session
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Calculations for, and laboratory measurements of a multistage labyrinthine baffle for SMEI
The spaceborne Solar Mass Ejection Imager (SMEI) is scheduled for launch into near-earth orbit (>800 km) in early 2003. Three SMEI CCD cameras on the zenith-oriented CORIOLIS spacecraft cover most of the sky each 100-minute orbit. Data from this instrument will provide precision visible-light photometric maps. Once starlight and other constant or slowly varying backgrounds are subtracted, the residue is mostly sunlight that has Thomson-scattered from heliospheric electrons. These maps will enable 3-dimensional tomographic reconstruction of heliospheric density and velocity. The SMEI design provides three cameras, one of which views to within 18 degrees of the solar disk with a field of view 60° long by 3° wide. Placed end-to-end, three fields of view then cover a nearly 180° long strip that sweeps out the sky over each orbit. The 3-dimensional tomographic analysis requires 0.1% photometry and background-light reduction below one S10 (the brightness equivalent of a 10th magnitude star per square degree). Thus 10-15 of surface-brightness reduction is required relative to the solar disk. The SMEI labyrinthine baffle provides roughly 10-10 of this reduction; the subsequent optics provides the remainder. We describe the baffle design and present laboratory measurements of prototypes that confirm performance at this level.
Inclusion of the CSSS magnetic field calculation into the UCSD tomograhic solar wind model
Tamsen Dunn, Pierre Paul Hick, Bernard V. Jackson, et al.
Tomographic techniques developed at UCSD over the last few years incorporate a kinematic model of the solar wind to determine and forecast the large-scale three-dimensional extents of velocity and density using interplanetary scintillation (IPS) observations or Thomson scattering brightness data. In this paper, we introduce magnetic field calculations from the Stanford Current-Sheet Source Surface (CSSS) model into our kinematic model. The CSSS model is used to extrapolate the photospheric magnetic field to a source surface at 15 solar radii (Rs). The UCSD kinematic model convects magnetic field from 15 Rs out to and beyond Earth. We compare the results with in situ data near Earth. The spatial relationship between the heliospheric current sheet and coronal mass ejections (CMEs) is shown in remote views of the inner heliosphere
121.6-nm stray light reduction methods for solar wind characterization instruments
Kamil A. Moldosanov, Reinhold Henneck, Michael A. Samsonov, et al.
In satellite-borne particle characterization instruments, for example, in the solar wind charge-energy-mass spectrometers and ion traps, there is a need to suppress the effect of the 121.6 nm Lyman-alpha line of the hydrogen spectrum, the most intensive line of the solar UV radiation resulting in high level of the detector’s noise. To reduce this effect, the electrodes of instruments are usually covered with electroconductive light-absorptive coatings having low reflectivity at the wavelength of 121.6 nm. In this paper the physical mechanisms are considered applicable to reduce the reflectivity of the A1-based coatings to be applied on electrodes of the particle analyzing instruments. Particular emphasis has been given to the role of three phenomena: (i) multiple light scattering light traps of the rough surface, (ii) diffraction of the incident light at the rough surface of the coating, and (iii) electron scattering in a skin layer. It is presented the behavior of reflectivity of the A1-based coating in the course of mechanical and environmental tests simulating standard shipping, storage, launching, flight, and operating conditions of the space equipment. The noise measurements of the Faraday cups used on board the INTERBALL-1 mission are also given. As the hydrogen is the most prevalent substance in the Universe, perhaps, the 121.6 nm stray light problem is the common one not only for the solar wind missions and solar astrophysics telescopes, but also for the Far UV astronomy and future UV space astrophysics missions.
High Energy Observations
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Imaging with RHESSI
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA SMall EXplorer (SMEX) mission to study the acceleration and transport of high-energy electrons and nuclei in solar flares. This is done using high spatial (2.3 arcsec) and high spectral (~1 keV) resolution imaging spectroscopy of X-rays and gamma rays between 3 keV and 17 MeV. Such an energy range includes ~10-30MK thermal emission, non-thermal hard X-ray bremsstrahlung from accelerated electrons, and gamma-ray lines from accelerated nuclei. RHESSI's imaging is based on a set of rotating modulation collimators. Each of the nine subcollimators uses a pair of widely separated (1.55m) grids, mounted on a rotating spacecraft. Each grid in turn consists of a large number of parallel, equispaced, X-ray-opaque slats. A corresponding set of nine high-resolution cooled germanium detectors determines the energy and arrival time of each detected photon. As the spacecraft rotates at ~15 rpm, the grid pairs time-modulate the detected X-ray flux in a manner sensitive to the morphology and location of the X-ray source(s). Post-analysis then reconstructs the image from the set of time-modulated light curves. This paper reviews the RHESSI imaging instrumentation, data analysis approach, imaging concept and early indications of in-flight performance.
RHESSI imager and aspect systems
Alex Zehnder, Jacek Bialkowski, F. Burri, et al.
RHESSI uses nine Rotating Modulation Collimators (RMCs) for imaging, each consisting of a pair of grids mounted on the rotating spacecraft. The angular resolutions range from 2.3 arcsec to 3arcmin. The relative twist between the two grids of each pair is the most critical parameter. It must be less than 20 arcsec for the finest grid. After precision alignment, it is monitored by the Twist Monitoring System (TMS) to a few arcsec. The Sun-pointing must be known better than 0.4 arcsec for the image reconstruction. This is achieved by the Solar Aspect System (SAS), which consists of a set of three Sun sensors. Each sensor is focusing the filtered Sun light onto a linear CCD. The onboard Aspect Data Processor (ADP) selects the 6 limb positions, which over-define the pointing offset of the Sun center in respect to the imaging axis of the imager. The Roll Angle System (RAS) continuously measures the roll angle of RHESSI within arcmin accuracy. The RAS is a continuously operating CCD star scanner. The time of the passage of a star image over the CCD is recorded and defines the roll angle, comparing its pixel position and amplitude with a star map.
RHESSI aspect system and in-flight calibration
Martin Fivian, Reinhold Henneck, Alex Zehnder
Precise knowledge of the pointing and the roll angle of the rotating spacecraft is needed in order to reconstruct images with 2 arcsec resolution using the modulation patterns seen on each of the detectors of the bi-grid rotating collimators. Therefore, the aspect system consists of two subsystems of sensors, the Solar Aspect System (SAS) and Roll Angle System (RAS). The transmitted data consists of Solar limb data from the SAS (CCD pixels around the intersection of a Solar image with three linear CCDs) and Star event data from the RAS (CCD pixels induced by passages of Star images over a linear CCD). In order to meet the RHESSI requirements, the reconstructed pointing needs to be ≤ 0.4 arcsec (rms) relatively (≤ 1 arcsec absolutely) and the determination of the roll angle needs to be better than 1 arcmin (rms). Beside of understanding and calibrating each sensor, the error budget on the aspect system requires an alignment of the relevant features of the 1.55 m extended telescope on a micron level. This could be achieved by a combination of on-ground and in-flight calibration.
EUV solar spectroscopic explorer (ESSEX): mission concept for a next-generation imaging spectrograph
Donald M. Hassler, Craig E. DeForest, David C. Slater
We discuss a mission concept (ESSEX) for probing energy and mass transport in the solar atmosphere. The primary instrument on ESSEX is a high-speed EUV imaging spectrograph designed to extract plasma diagnostics from the small-scale, rapidly varying events that are thought to heat the solar atmosphere. We argue that spectral resolution is required to determine the physics that underlies the spectacular solar coronal images returned by TRACE and other EUV imaging telescopes. Previous and current spectrographs are severely limited in time resolution, and we present two rapid imaging spectrograph designs that are optimized for different tasks: the ESSEX spectrograph, intended as a pure science instrument to identify the physical mechanisms of energy and mass transport in generic solar features; and a synoptic spectrograph, intended as an operational instrument to quantify momentum and energy release in coronal mass ejections and filament liftoff events. If flown, ESSEX will provide high cadence observations required to trace the flow of energy through reconnection and wave motion in the solar atmosphere. It will achieve sub-arcsecond resolution in the transition region and corona with both spectroscopy and imaging over a continuous temperature range from 10,000 K to 10 million K, and will sample chromospheric wave motion at frequencies over 100 Hz.
Cleanliness and calibration stability of UV instruments on SOHO
Optical instruments for solar observations from space have in the past suffered from degradation of responsivity caused by contamination from various materials used in spacecraft and instrument construction. This was particularly detrimental in the ultraviolet range of the spectrum where the solar irradiance is weak, compared to the visible, yet strong enough to cause polymerization of organic contaminants on optical surfaces that are continuously exposed. The Solar and Heliospheric Observatory (SOHO) mission could largely avoid such effects. Material selection and special design features of instruments and spacecraft contributed mostly to this success. The various kinds of remote sensing instruments on SOHO have achieved a stability of their responsivity through special cleanliness requirements. This contribution will highlight those design aspects which are generally useful for future solar missions. Analysis of instrument responsivity data shows that under these circumstances the stability was actually not limited by contamination but by the instabilities inherent to the present detector technology.
Radio
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Progress on the frequency agile solar radiotelescope
The Frequency Agile Solar Radiotelescope (FASR) is a solar-dedicated, ground based, interferometric array optimized to perform broadband imaging spectroscopy from ~ 0.1-30+ GHz. It will do so with the angular, spectral, and temporal resolution required to exploit radio emission from the Sun as a diagnostic of the wide variety of astrophysical processes that occur there. FASR represents a major advance over existing radioheliographs, and is expected to remain the world's premier solar radio instrument for two decades or more after completion. FASR will be a versatile and powerful instrument, providing unique data to a broad users community. Solar, solar-terrestrial, and space physicists will exploit FASR to attack a broad science program, including problems of fundamental interest: coronal magnetography, solar flares and particle acceleration, drivers of space weather, and the thermal structure and dynamics of the solar atmosphere. A design study and implementation planning are underway. Recent progress is reviewed here.
Solar radioastronomy with the LOFAR (low-frequency array) radio telescope
The Low Frequency Array (LOFAR) will be a radio astronomy interferometric array operating in the approximate frequency range 10-240 MHz. It will have a large collecting area achieved using active dipole techniques, and will have maximum baselines of up to 500 km to attain excellent spatial resolution at long wavelengths. The Sun will always be in LOFAR's beam during daylight hours, and particularly during periods of high solar activity the Sun will be a prominent (and highly variable) feature of the low-frequency sky. A diverse range of low-frequency emissions is generated by the Sun that carry information about processes taking place in the Sun's atmosphere. Study of these emissions with LOFAR will make possible major advances in our understanding of particle acceleration and shocks in the solar atmosphere, and of coronal mass ejections and their impact on the Earth. In this paper we summarize LOFAR's capabilities and discuss the solar science that LOFAR will address.
Solar wind imaging facility (SWIFT) for space weather research
Masayoshi Kojima, Munetoshi Tokumaru, Ken-ichi Fujiki, et al.
The interplanetary scintillation (IPS) method can observe the dynamics and structure of the solar wind in three dimensions with a relatively short time cadence (<1 day) using IPS radio sources distributed over the sky. Because of this advantage over in situ measurements, we have been conducting multi-station 327 MHz IPS observations at the Solar-Terrestrial Environment Laboratory. The IPS measurement is a line-of-sight integration which is a convolution of the solar wind structures, the distance of these from the Earth and other diffraction effects present along the line of sight. We have recently succeeded in developing a method to deconvolve the line-of-sight integration effects using a computer-assisted-tomography (CAT) technique to obtain solar wind speed and electron density fluctuations. The CAT analysis not only retrieves three-dimensional solar wind parameters, but also provides better spatial resolutions than previous analysis techniques. The present IPS system at STELab observes several tens of IPS sources a day. To make solar wind observations with higher spatial and temporal resolution using the CAT method, we need more perspective views of the solar wind. Therefore, we are planning a new UHF antenna with an effective collecting area of 5500m^2 that will observe more than 100 IPS sources per day. The antenna is designed with a tolerance for radio noise interference and high aperture efficiency. Based on the successful development of the IPS CAT analysis, we are presently continuing a US-Japan cooperative project for space weather research between UCSD/CASS and STELab. This project with the new antenna will enhance IPS/US cooperation including future comparative analyses of data from the Solar Mass Ejection Imager (SMEI) and from STEREO.
Poster Session
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Site testing issues for the Frequency Agile Solar Radiotelescope (FASR)
The Frequency Agile Solar Radiotelescope (FASR) will be a broadband synthesis-imaging array with 3-km or larger baselines, operating over a broad frequency range of 0.1-30 GHz. The instrument demands a site with low levels of Radio Frequency Interference (RFI) over this entire band. The site also must be large enough to accommodate the expected size of the array configuration and ideally would provide room to grow with future upgrades. The site must have a benign environment in which at least 100 separate elements will operate with little degradation and weather-related downtime. Several sites in the U.S. are being considered. We discuss what criteria are being used to assess the sites, and give some initial results of testing some of the sites.
Imaging capabilities of the Frequency Agile Solar Radiotelescope
Stephen White, Jeongwoo Lee, Markus A. Aschwanden, et al.
The Frequency Agile Solar Radiotelescope (FASR) will observe the Sun over a wide range of radio frequencies and make high spatial resolution images at many frequencies nearly simultaneously. FASR will need to be able to observe both the very bright, usually compact emission from solar flares as well as much fainter fluctuations in the solar chromosphere across a broad range of spatial scales (from 1 arcsec to 1 degree) at high time resolution, and these constraints impose severe requirements on telescope design. We discuss the problem of imaging the Sun at radio wavelengths and present simulations of imaging the thermal free-free emission from the Sun's atmosphere using models based on EUV data.
Balloon Missions
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SUNRISE: a balloon-borne telescope for high resolution solar observations in the visible and UV
Sami K. Solanki, Achim M. Gandorfer, Manfred Schuessler, et al.
Sunrise is a light-weight solar telescope with a 1 m aperture for spectro-polarimetric observations of the solar atmosphere. The telescope is planned to be operated during a series of long-duration balloon flights in order to obtain time series of spectra and images at the diffraction-limit and to study the UV spectral region down to ~200 nm, which is not accessible from the ground. The central aim of Sunrise is to understand the structure and dynamics of the magnetic field in the solar atmosphere. Through its interaction with the convective flow field, the magnetic field in the solar photosphere develops intense field concentrations on scales below 100 km, which are crucial for the dynamics and energetics of the whole solar atmosphere. In addition, Sunrise aims to provide information on the structure and dynamics of the solar chromosphere and on the physics of solar irradiance changes. Sunrise is a joint project of the Max-Planck-Institut fuer Aeronomie (MPAe), Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofi sica de Canarias, La Laguna, Tenerife. In addition, there are close contacts with associated scientists from a variety of institutes.
Near-infrared chromospheric observatory (NICO)
Barry Labonte, David M. Rust, Pietro N. Bernasconi, et al.
NICO, the Near Infrared Chromosphere Observatory, is a platform for determining the magnetic structure and fources of heating for the solar chromosphere. NICO, a balloon-borne observatory, will use the largest solar telescope flying to map the magnetic fields, velocities, and heating events of the chromosphere and photosphere in detail. NICO will introduce new technologies to solar flight missions, such as wavefront sensing for monitoring telescope alignment, real-time correlation tracking and high-speed image motion compensation, and wide aperture Fabry-Perot etalons for extended spectral scanning.
Poster Session
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Software design for a balloon-borne solar telescope
This paper introduces our control software design for a tracing system of precise pointing on a balloon-borne telescope to observe the active details on the solar surface. The telescope is an equatorial one with 80 cm in diameter. Borne by balloon, it works at 30 km above the sea level so as to get rid of the image disturbance due to atmosphere. The system contains three parts: basket control, telescope control and tip-tilt control. For telescope control, the crude sensors for pointing detection are two rotating transformers, while the fine sensors two linear CCDs which produce the error signals of pointing. An inserted-type industry-control computer PC104 completes the position close-loop and then drives the servo amplifiers to carry out pointing, searching and tracing automatically. Due to the fact that the position control loop is closed with an improved digital PID arithmetic, the adjustment of the telescope may respond rapidly, therefore the telescope can precisely follow the Sun on the balloon. Simulation test shows that the tracing accuracy may reach as high as 4" (RMS).
Space Missions and Instrumentation I
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Solar Orbiter: a mission overview and status update
Bernhard Fleck, Richard G. Marsden
Approved in October 2000 by ESA's Science Programme Committee as a flexi-mission and re-confirmed in May 2002 as an element in the new ESA science programme "Cosmic Vision", the Solar Orbiter will study the Sun and unexplored regions of the inner heliosphere from a unique orbit that brings the probe to within 45 solar radii of our star, and to solar latitudes as high as 38 degrees. The scientific payload to be carried by the Solar Orbiter will include both remote-sensing instruments and an in situ package. Launch is currently scheduled for 2012. Given the technical challenges associated with this mission, it is essential that key technologies requiring significant development be identified as early as possible. ESA has therefore set up Payload Working Groups whose task it is to address potential problem areas arising as a result of the extreme thermal and radiation environment and to identify necessary technological developments.
Photon sieves as EUV telescopes for Solar Orbiter
Guy Edouard Artzner, Jean Pierre Delaboudiniere, Xueyan Song
We elaborate about obtaining images of the solar disc and of the solar corona at discrete wavelengths along the EUV emission solar spectrum on board the Solar Orbiter spacecraft. Refractive optics cannot be used. The thermal load is twenty five times higher than on a near Earth orbit. As on one side the efficiency of a stenopeic device is too low, and as on the other side mirrors exposed directly to the light and to the particles emitted by the Sun may severely degrade during time, we investigated using the EUV analog of a Fresnel lens, i.e. a photon sieve. An opaque self supporting flat piece of heat resistant metal let the solar light shine through a large numbers of a few thousand holes properly designed in positions and diameters in order to obtain constructive interferences at some focus. We report about practical experiments in the visible.
Ultraviolet and visible-light coronagraphic imager (UVCI) for HERSCHEL (helium resonance scattering in corona and heliosphere
Silvano Fineschi, Ester Antonucci, Marco Romoli, et al.
The HERSCHEL (HElium Resonance Scattering in the Corona and HELiosphere) Sun-Earth Sub-Orbital Program is a proposed sounding-rocket payload designed to investigate helium coronal abundance and solar wind acceleration from a range of solar source structures by obtaining simultaneous observations of the electron, proton and helium solar coronae. HERSCHEL will provide the first measurements of the coronal helium abundance in source regions of the solar wind, thus bringing key elements to our understanding of the Sun-Earth connections. The HERSCHEL instrument package consists of the Extreme Ultraviolet Imaging Telescope (EIT) for on-disk coronal observations and the Ultraviolet and Visible-light Coronagraphic Imager (UVCI) for off-limb observations of the corona. The UVCI is an externally occulted, reflecting coronagraph with an off-axis Gregorian telescope. UVCI will be able to take coronal images at heliocentric heights comprised between 1.2 to 3.5 solar radii of a) K-corona polarized brightness (pB); b) H I Lyman-α, 121.6 nm, line-emission; c) He II Lyman-α, 30.4 nm, line. The key element in the UVCI instrument concept is that the mirrors with multilayer coatings optimized for 30.4 nm still have good reflectivity at 121.6 nm and in the visible. The optical design concept for the UVCI instrument will be discussed, together with its expected optical and throughput performances.
CCD cameras for the polarimetric channels of HERSCHEL
A new concept CCD camera is currently under development at the XUVLab of the Department of Astronomy and Space Science of the University of Florence. This CCD camera is the proposed detector for the broadband visible light polarimetric channels of the UVCI coronagraph of HERSCHEL and of Solar Orbiter space missions. The main features of this camera are a high level of versatility and a fast pixel that will satisfy the requirements of both the space missions. Within this project, a versatile CCD controller has been produced with interesting and innovative features: it allows the selection of all the parameters related to charge transfer and CCD readout and therefore it allows the use of virtually any CCD sensor. The software interface is LabVIEW 6i based and it will allow both local and remote control and display.
Solar Probe: Mission to the Sun--overview and status report
The Solar Probe mission is an unprecedented exploration of the inner heliosphere, which will achieve unique science by flying over the pole of the Sun and as close to the Sun's surface, through the solar corona, as is technologically feasible today. It will first travel to Jupiter for a gravity assist, leave the ecliptic plane, fly over the Sun's poles to within 8 solar radii, and reach perihelion over the equator at 4 solar radii. A unique aspect of the Solar Probe orbit is that the trajectory is orthogonal to the Sun-Earth line during perihelion passage so that there is continuous radio contact throughout the flyby. Two perihelion passes are planned, the first near the 2014 solar minimum and the second near the 2019 solar maximum. This orbit ensures that the mission will probe both the high speed solar wind streams and the equatorial low-speed streams. Although NASA recinded the 1999 Solar Probe Announcement of Opportunity (AO 99-OSS-04) in early 2001, Solar Probe is still very much alive and community support for the mission is strong. In the fall of 2001, Congress earmarked $3M for Solar Probe and instructed NASA to consolidate the Solar Probe management within the existing SEC/LWS program. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is currently reviewing the mission and conducting an Engineering Assessment Study to be released later this year. Both the NRC Decadal Survey Committee and the SEC Roadmap Committee have strongly endorsed Solar Probe and recommended that it be "implemented as soon as possible".
Poster Session
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Solar Space Telescope data format analysis and configuration
Lihong Geng, Caihong Sun, Jingyu Wang, et al.
The Space Solar Telescope (SST) with five payloads onboard is now under researching, developing and manufacturing. These payloads with different observation modes and different original data formats will produce up to 50GB scientific data per day. On board data processing units, such as integration, compression and computation unit, are needed to reduce the data amount to about 10GB to fit the ability of X-band scientific data translating system. And data encoding unit is also necessary to transfer the data into transmittable data format. So the scientific data will have different data formats. In Researching and Developing the SDPU of the SST, how to manage the science data storied in Data Storage Unit (DUS) has become one of the important issues, for the data format should be very convenient for post processing and data recovering on ground. In this paper, the detailed science data flow, corresponding to different observation modes, different data processing sequences and different data formats, will be discussed. Tables and figures are also used to show preliminarily the complex configurations of SST data format.
Structural analysis and thermal influence of Space Solar Telescope
Chen Zhiping, Shimo Yang, Qi-qian Hu
The Space Solar Telescope (SST), the first astronomical satellite proposal in China, is under researched, developed and manufactured. It is designed to make observations of transient and steady state solar hydrodynamic and magnetohydrodynamic processes. The space-frame of SST provides the mechanical interface between the telescope and instruments, and it is a crucial linker for all the optical, mechanical, and electronic subsystems. Therefore, the structural parts of SST must satisfy sufficient strength, stiffness, and thermal stability requirements of optical and other subsystems under the space environment and in the launching process. This paper first describes the static and dynamic analyses of the original structure by the Finite Element Analysis (FEA) tool. Then, it presents the structure optimization with the objective to enhance the natural frequency under the total weight unchanged. Finally, it verifies the optimized structure and analyzes the thermal influence of SST. The analysis results and structural responses with all the payloads being considered are discussed and illustrated in this paper. Now, SST is in the phase of test and key technology tackle, and some main parts have been finished. All analysis results shown in this paper will be applied to further research and fabrication.
Polarimetry of the Solar Atmosphere I
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SOLIS: an innovative suite of synoptic solar instruments
Christoph U. Keller, John W. Harvey, Mark S. Giampapa
SOLIS (Synoptic Optical Long-term Investigations of the Sun) is a suite of three innovative instruments under construction that will greatly improve ground-based synoptic solar observations. The Vector Spectromagnetograph (VSM) is a compact, high-throughput vector-polarimeter with an active secondary mirror, an actively controlled grating spectrograph, and two high-speed cameras with silicon-on-CMOS-multiplexer hybrid focal plane arrays. It will measure the magnetic field strength and direction over the full solar disk within 15 minutes. The Full-Disk Patrol (FDP) takes full-disk solar intensity and Doppler images in various spectral lines and in the continuum at a high cadence through liquid-crystal tuned birefringent filters. The Integrated Sunlight Spectrometer (ISS) uses a fiber-fed spectrograph to measure minute changes of the Sun-as-a-star in many spectral lines. A high degree of automation and remote control provides fast user access to data and flexible interaction with the data-collection process. SOLIS is currently in the final assembly phase and will become operational early in 2003.
Motivation; design, and development of 12-um imaging stokes polarimeters for solar magnetic field studies
Drake Deming, Donald E. Jennings, George H. McCabe, et al.
We discuss the scientific motivations, design considerations, and development status of imaging Stokes polarimeters based on the extremely Zeeman-senstive infrared emission line of MgI at 12.32 μm. The resolved Zeeman splitting exhibited by this far-infrared line enables significant progress on many problems in solar physics. These problems include vertical gradients in field strength, the magnetic structure of sunspots, the nature of magnetic energy release associated with solar flares, the measurement of horizontal currents in solar active regions, improved measurements of vertical currents, direct measurement of photospheric reconnection, the occurrence and nature of weak magnetic fields, and other problems. We discuss why 12 μm measurements are well suited to these investigations, and we comment on the capability of current instrumentation to enable these studies. Several instruments currently exist to perform 12 μm Stokes polarimetry: a Fabry-Perot system, a grating spectrometer, and the McMath-Pierce Fourier transform spectrometer (which remains crucial for many aspects). We elaborate on some design considerations and development issues, and discuss the optimal approach to be taken in future 12 μm imaging Stokes polarimetry.
Polarimetry of the Solar Atmosphere II
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The ATST near-IR spectropolarimeter
The development of new solar IR instrumentation in the past decade had opened new windows of opportunity for solar physics research which were not accessible before. Many spectral lines in the near-IR wavelength range from 1 to 2 microns offer powerful diagnostics for the study of solar magnetism in the photosphere, the chromosphere, and the corona. Significant progress and breakthroughs were made in areas such as the generation of weak background magnetic fields by small-scale surface dynamos, the physics of the sunspot, and the direct measurement of magnetic fields in the corona. The combination of these new IR diagnostics tools, and the unprecedented 4-meter aperture and versatile photospheric and coronal capabilities of the Advanced Technology Solar Telescope (ATST), will greatly enhance our capability to study the Sun. It further promises breakthrough observations that can help to resolve many of the long-standing mysteries of solar physics. The instruments for the ATST will need to accommodate a broad range of science subjects, each with its unique observational requirements. This paper examine the near-IR instrumentation required to achieve the ATST science goals, and present conceptual designs of a near-IR SpectroPolarimeter (NIRSP) aimed at addressing the new challenges of observational solar physics brought upon by the ATST.
IRIM: an imaging magnetograph for high-resoultion solar observations in the near-infrared
The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near-infrared (NIR)observations of the Sun. IRIM will provide high spatial resolution (0.2" per pixel image scale), high temporal resolution (1-2 minutes), moderate spectral resolution (14.0 pm), and high magnetic sensitivity covering a substantial field-of-view (FOV: 170" circular). The bandpass of the instrument is reduced in three steps while still providing high transmission: (1) a 4 nm interference filter, (2) a 0.25 nm Lyot-filter, and (3) a 14.0 pm tunable Fabry-Perot etalon. The innovative NIR Lyot-filter was developed at the New Jersey Institute of Technology (NJIT) and is currently being assembled at Cambridge Research Instruments. It is the first of its kind and provides a large angle of acceptance, thus solving many problems encountered with dual Fabry-Perot systems. The two-dimensional line profiles will be recorded by a 1024 × 1024 pixel, 12-bit Complex Metal Oxide Semiconductor (CMOS) focal plane array (FPA) manufactured by Rockwell Scientific Imaging, which can obtain images at a rate of 50 fps. IRIM will utilize the remodelled Coude-feed of the 65 cm vacuum telescope at the Big Bear Solar Observatory (BBSO) and will benefit from an image stabilization and correction system of independently operating Correlation Tracking (CT) and Adaptive Optics (AO) systems.
Polarimeter for the study of magnetic fields in prominences
Arturo Lopez Ariste, Steven Tomczyk, Meir Semel, et al.
We report on a new spectropolarimeter for the measurement of vector magnetic fields on prominences using the HeD3 line in the Evans Solar Facility at the Sacramento Peak Observatory.
Ground Based Telescopes and Instruments I
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Design and development of the Advanced Technology Solar Telescope
High-resolution studies of the Sun's magnetic fields are needed for a better understanding of solar magnetic fields and the fundamental processes responsible for solar variability. The generation of magnetic fields through dynamo processes, the amplification of fields through the interaction with plasma flows, and the destruction of fields are still poorly understood. There is still incomplete insight as to what physical mechanisms are responsible for heating the corona, what causes variations in the radiative output of the Sun, and what mechanisms trigger flares and coronal mass ejections. Progress in answering these critical questions requires study of the interaction of the magnetic field and convection with a resolution sufficient to observe scales fundamental to these processes. The 4m aperture Advanced Technology Solar Telescope (ATST) will be a unique scientific tool, with excellent angular resolution, a large wavelength range, and low scattered light. With its integrated adaptive optics, the ATST will achieve a spatial resolution nearly 10 times better than any existing solar telescope. Building a large aperture telescope for viewing the sun presents many challenges, some of the more difficult being Heat control and rejection Contamination and scattered light control Control of telescope and instrument polarization Site selection This talk will present a short summary of the scientific questions driving the ATST design, the design challenges faced by the ATST, and the current status of the developing design and siting considerations
Multiple-etalon systems for the Advanced Technology Solar Telescope
G. Allen Gary, K. S. Balasubramaniam, Michael Sigwarth
Multiple etalon systems are discussed that meet the science requirements for a narrow-passband imaging system for the 4-meter National Solar Observatory (NSO)/Advance Technology Solar Telescope (ATST). A multiple etalon system can provide an imaging interferometer that works in four distinct modes: as a spectro-polarimeter, a filter-vector magnetograph, an intermediate-band imager, and broadband high-resolution imager. Specific dual and triple etalon configurations are described that provide a spectrographic passband of 2.0-3.5 pm and reduce parasitic light levels to 10-4 as required for precise polarization measurement, e.g., Zeeman measurements of magnetic sensitive lines. A TESOS-like (Telecentric Etalon SOlar Spectrometer) triple etalon system provides a spectral purity of 10-5. The triple designs have the advantage of reducing the finesse requirement on each etalon; allow the use of more stable blocking filters, and have very high spectral purity. A dual-etalon double-pass (Cavallini-like) system can provide a competing configuration. Such a dual-etalon design can provide high contrast. The selection of the final focal plane instrument will depend on a trade-off between an ideal instrument and practical reality. The trade study will include the number of etalons, their aperture sizes, complexities of the optical train, number of blocking filters, configuration of the electronic control system, computer interfaces, temperature controllers, etalon controllers, and their associated feedback electronics. The heritage of single and multiple etalon systems comes from their use in several observatories, including the Marshall Space Flight Center (MSFC) Solar Observatory, Sacramento Peak Observatory (NSO), and Kiepenheuer-Institut für Sonnenphysik (KIS, Germany), Mees Solar Observatory (University of Hawaii), and Arcetri Astrophysical Observatory (Italy). The design of the ATST multiple etalon system will benefit from the experience gained at these observatories.
The ATST seeing monitor: February 2002 observations at Fuxian Lake
We describe a solar seeing monitor used for the site testing for the 4 meter US Advanced Technology Solar Telescope and the 1 meter Yunnan Observatory Solar Telescope. It has two parts: a solar Differential Image Motion Monitor (S-DIMM) and a linear array of 6 solar scintillometers (SHABAR= SHAdow BAnd Ranger). The results obtained by both methods are compared on the basis of observations obtained in February 2002 at the Yunnan Observatory Fuxian Lake solar station. Analysis showed that these two ways of measuring the Fried parameter give consistent results. We confirm earlier observations that showed that the boundary layer seeing over lakes is strongly suppressed. The amount of this boundary layer seeing depends on the temperature difference between lake and air and on the wind velocity. We have also carried out seeing observation along a 9.15 km horizontal path across the lake. The Cn2 values derived from these is consistent with the solar observations. They confirm the dependence of Cn2 on the lake-to-air temperature difference. From the SHABAR we find a typical scale height for the boundary layer seeing of 20 meters and from inter-comparison of the S-DIMM and SHABAR observations we derive an outer scale of turbulence of about 50 meters.
Environmental factors affecting solar seeing
Frank Hill, John W. Briggs, Steven L. Hegwer, et al.
We investigate a number of ideas about the effect of various topographical and climtatological factors on daytime seeing. Using the results of the CalTech site survey in southern California, we confirm that the presence of lakes and wind channels are beneficial for solar observing conditions. We do not find that proximity to the ocean is of benefit but is instead detrimental to seeing in the CalTech sample possibly due to the influence of the Los Angeles metropolitan area. We also study the effect of tree removal on the seeing at Sacramento Peak Observatory, and find that removing trees improved the average seeing by 25%. The effects of these and other factors will be further investigated with the ATST site survey.
Large open telescope: size-upscaling from DOT to LOT
The design characteristics of a large open telescope (LOT) are: (i) an open tower with only pure translations of the platform under wind load; (ii) an open telescope construction with extremely stiff geometry and drives; (iii) simple optics with easy aligning and testing, but nevertheless suitable for large auxiliary equipment like spectrographs.
Multiwavelength imaging system for the Dutch Open Telescope
Felix C.M. Bettonvil, Peter Suetterlin, Robert H. Hammerschlag, et al.
The Dutch Open Telescope (DOT) is an innovative solar telescope, completely open, on an open steel tower, without a vacuum system. The aim is long-duration high resolution imaging and in order to achieve this the DOT is equipped with a diffraction limited imaging system in combination with a data acquisition system designed for use with the speckle masking reconstruction technique for removing atmospheric aberrations. Currently the DOT is being equipped with a multi-wavelength system forming a high-resolution tomographic imager of magnetic fine structure, topology and dynamics in the photosphere and low- and high chromosphere. Finally the system will contain 6 channels: G-band (430.5 nm), Ca II H (K) (396.8 nm), H-α (656.3 nm), Ba II (455.4 nm), and two continuum channels (432 and 651 nm). Two channels are in full operation now and observations show that the DOT produces real diffraction limited movies (with 0.2" resolution) over hours in G-band (430.5 nm) and continuum (432 nm).
Ground Based Telescopes and Instruments II
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The SOLARC off-axis coronagraph
Jeff R. Kuhn, Roy Coulter, Haosheng Lin, et al.
A 0.5m aperture off-axis coronagraphic telescope is described. Its fabrication, imaging, and scattered light performance is discussed in the context of simple model expectations.
Imaging of the solar interior: possibilities and limitations
Alexander G. Kosovichev, Thomas L. Duvall Jr.
Helioseismic tomography is a promising new method for probing 3-D structures and flows beneath the solar surface. It is based on observation of solar acoustic waves, and provides great possibilities for studying the birth of active regions in the Sun's interior and for understanding the relation between the internal dynamics of active regions and chromospheric and coronal activity. We discuss observational requirements, challenges and limitations of this technique for investigating physical processes in the solar interior on their intrinsic spatial and temporal scales.
The 1-m Swedish solar telescope
Goran B. Scharmer, Klas Bjelksjo, Tapio K. Korhonen, et al.
We describe the 1-meter Swedish solar telescope which replaces the former 50-cm solar telescope (SVST) in La Palma. The un-obscured optics consists of a singlet lens used as vacuum window and two secondary optical systems. The first of these enables narrow-band imaging and polarimetry with a minimum of optical surfaces. The second optical system uses a field mirror to re-image the pupil on a 25 cm corrector which provides a perfectly achromatic image, corrected also for atmospheric dispersion. The adaptive optics system is integrated with the design of the telescope but is sufficiently flexible to allow future upgrades. It consists of a low-order bimorph modal mirror with 37 electrodes, allowing near-diffraction-limited imaging a reasonable fraction of the observing time on La Palma. The new telescope became operational at the end of May 2002 and has already proven to be the most highly resolving solar telescope ever built. In this paper, we describe its mechanical and optical design, the polishing and testing of the optics and the instrumentation in use or planned for this telescope.
Low-cost solar adaptive optics in the infrared
We have developed a low-cost adaptive optics system for solar observations in the infrared between 1 and 28 μm with the 1.5-m McMath-Pierce solar telescope. The 37-actuator membrane mirror and a fast tip-tilt mirror are controlled by a PC running Linux RedHat 7.1 that analyzes images from a 256 by 256 pixel, 1 kHz frame rate CCD camera. The total hardware cost is less than $25,000, and the system provides diffraction-limited performance under median seeing conditions above 2.3 μm. The single Pentium III processor provides enough computing power to analyze the 200 subapertures of the Shack-Hartmann wavefront sensor in real time. We describe the hardware and software implementations and show results from the first tests at the telescope.
Poster Session
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Image slicer integral field unit for solar telescope
Integral Field Spectroscopy (IFS) can provide two-dimensional spatial and one spectral information for spectroscopic observation simultaneously. This is important for solar observatory because of the nature of the extended object of the solar observatory. Integrated Field Unit (IFU) is the key and basic tool for IFS. An innovative IFU was designed at National Solar Observatory which will deliver good image quality at visible (0.39 - 1.0 mm) and near infrared (1.0-1.6 mm) wavelength ranges simultaneously. The IFU is realized by using image slicer and will take the full advantage of the excellent corrected image of a high order Adaptive Optics (AO) and provide powerful image spectroscopic ability for a spectrograph/ polarimeter. This may be the first time that advanced IFU will achieve at visible and near infrared simultaneously and be used for solar observatory. A unique design is a key importance to ensure that the IFU image slicer can work at visible and near infrared wavelengths with excellent optical performance. The IFU design is discussed in detail in this paper. It is demonstrated that the IFU image slicer technique is suitable for both visible and near infrared solar observatories and will be particularly useful for 4 or 8-meter telescopes.
Tilt-correction adaptive optical system for Solar Telescope of Nanjing University
Changhui Rao, Wenhan Jiang, Cheng Fang, et al.
A tilt-correction adaptive optical system installed at 430mm Solar Telescope at Nanjing University has been in operation. It is made up of a tip-tile mirror, a correlation tracker and an imaging CCD camera. The Absolute Difference algorithm is used in order to detect image motion in the correlation tracker. The sampling frequency of the system is 419Hz. In this paper, the configuration of the system is described. The observation results are reported. Furthermore, the performance of the system is analyzed. The residual jitter of 0.14arcsec has been achieved. The error rejection bandwidth of the system can be adjusted in the range from 5Hz to 28Hz according to the beacon size and the strength of the atmospheric turbulence.
Ground Based Telescopes and Instruments II
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Adaptive optics system for the new Swedish solar telescope
The 1-meter Swedish solar telescope is a new solar telescope that was put in operation on the island of La Palma in the Canary Islands at the end of May 2002. The goal of this telescope is to reach its diffraction limited resolution of 0.1 arcsec in blue light. This has already been achieved by use of a low-order adaptive optics (AO)system. This paper describes the AO system initially developed for the former 50-cm Swedish Vacuum Solar Telescope (SVST) and further improved for the new telescope. Both systems use a combination of bimorph modal mirrors and Shack-Hartmann wavefront sensors. Unique to these systems are that they rely on a single workstation or a PC to do all the computations required to extract and pre-process the images, measure their positions using cross correlation techniques and for controlling the deformable mirror. This is in the present system possible by using the PERR instruction available on Compaq's Alpha architecture and in the new system using the PSADDBW instruction, available on Pentium 4 and Athlon processors. We describe both these systems with an emphasis on the performance, the ease of support and upgrades of performance. We also describe the optimization of the electrode geometry for the new 37-electrode bimorph mirror, supplied by AOPTIX Technologies, Inc., for controlling Karhunen--Loeve modes. Expected performance, based on closed-loop simulations, is discussed.
Poster Session
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Strategies for prime focus instrumentation in off-axis Gregorian systems
Roy Coulter, Jeff R. Kuhn, Haosheng Lin
A new generation of off-axis telescopes has been proposed to address a number of high dynamic range problems in astrophysics. These systems present unusual problems and opportunities for the instrument designer. We will discuss some of the issues that must be resolved when placing instrumentation at the prime focus. The heat stop and occulter systems for the SOLARC off-axis coronagraph will be used to illustrate strategies for solar telescope applications.
Diverse-phase speckle inversion applied to data from the Swedish 1-meter solar telescope
We report on the use of a new joint phase diverse speckle code, an implementation of a method where a single object and individual phases are estimated from several pairs of phase diverse data. The code was used on 430.5 nm G-band data collected with the newly installed Swedish 1-meter solar telescope in La Palma, equipped with a low-order adaptive optics system. We describe the algorithm briefly, show wavefront statistics and object estimates from the processing and discuss the results. We demonstrate a resolution of 0.12 arc seconds for a time sequence and a large field of view, which is a break-through for ground based solar telescopes.
High-speed H-alpha camera and a real-time image processing system for solar observations
Yoichiro Hanaoka, Motokazu Noguchi, Takashi Sakurai, et al.
We have developed a new digital imaging system for the Hα imager of the Solar Flare Telescope at Mitaka, NAOJ, for high-cadence observations of solar flares. To resolve individual spikes elementary bursts) of impulsive solar flares requires a time resolution within 1 s and a spatial resolution of about 1", and the high-speed Hα camera realized them. Such high-resolution observations produce huge amount of data, and it has been the major difficulty to construct a high-cadence system. Generally the amount of data from solar optical observations is huge, because they are multi-dimensional (in space/time/wavelength/polarization status). Efficient real-time processing of observational data is essentially important to extract meaningful information from the raw data. Recent advances in computer technology have made possible to handle vast data with a small computer. Therefore, firstly we have developed a PC-based flexible real-time image processing system, which is applicable to various real-time data processings required for solar optical observations. The high-speed Hα camera is developed based on this system. In this paper, the real-time image processing system and the high-speed Hα camera system are described as well as the actual operation of the Hα camera.
Multiwavelength high-speed video spectroheliograph
A high-speed video spectroheliograph was developed for imaging spectroscopy observations in multi-wavelength bands. It is attached to the focal plane of the spectrograph of the 60 cm Domeless Solar Telescope at Hida Observatory, Kyoto University. Although to take spectroheliograms needs some time to scan the solar image on the slit, a spectroheliograph gets spectral information co-temporally without suffering image blurrings by the seeing effect. Therefore, a spectroheliograph is suitable to obtain a data cube (spatial 2-D + spectral 1-D) for quantitative spectral analyses such as velocity field calculations. In our spectroheliograph system, up to three CCD video cameras can be attached to the spectrograph, and we can simultaneously observe up to three wavelength bands, for example, Ca II K/G-band/Hα,with three CCD video cameras, owing to the wide wavelength coverage of the spectrograph. Therefore, heliograms at different heights in the solar atmosphere can be obtained simultaneously. Images from the cameras are digitized by a frame grabber to 512 (4.3' along the slit) pixels × 256 (along the dispersion, typically 24 Å wide) lines and processed by a PC with a frame rate of 30 frames s-1. Therefore, it takes only 17 s to obtain a set of 512 × 512 pixel heliograms, which cover the field of view of 4.3'×4.3'.
Optical design of a high-order adaptive optics for the NSO Dunn Solar Telescope and the Big Bear Solar Observatory
The National Solar Observatory (NSO) and the New Jersey Institute of Technology are jointly developing high order solar Adaptive Optics (AO) to be deployed at both the Dunn Solar Telescope (DST) and the Big Bear Solar Telescope (BBST). These AO systems are expected to deliver first light at the end of 2003. We discuss the AO optical designs for both the DST and the BBST. The requirements for the optical design of the AO system are as follows: the optics must deliver diffraction-limited imaging at visible and near infrared over a 190"×190" field of view. The focal plane image must be flat over the entire field of view to accommodate a long slit and fast spectrograph. The wave-front sensor must be able to lock on solar structure such as granulation. Finally, the cost for the optical system must fit the limited budget. Additional design considerations are the desired high bandwidth for tip/tilt correction, which leads to a small, fast and off-the-shelf tilt-tip mirror system and high throughput, i.e., a minimal number of optical surfaces. In order to eliminate pupil image wander on the wave-front sensor, both the deformable mirror and tip-tilt mirror are located on the conjugation images of the telescope pupil. We discuss the details of the optical design for the high order AO system, which will deliver high resolution image at the 0.39 - 1.6 μm wavelength range.
Space Missions and Instrumentation II
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Development of multilayer coatings for solar space experiments
Maria-Guglielmina Pelizzo, Alessandro Patelli, Piergiorgio Nicolosi, et al.
Deposition and characterization results of multilayer coatings optimized for HeII 30.4 nm high reflectivity will be presented. Additional characterization of reflectivity at HI Ly-α and in the visible spectral range has been also accomplished in order to investigate the performances of such coatings in view of their application to the UVCI instrument on board of ESA payload SOLO and to HERSCHEL, a sounding rocket experiment.
Grazing incidence objective grating spectro-imagers for EUV observations of the solar corona
Jean-Pierre Delaboudiniere, Igor A. Zhitnik, Marie-Francoise Ravet, et al.
Objective grating spectrometers have been used previously to image the sun in the EUV proving simultaneous images at several wavelengths. The grazing incidence variant of this type of instrument seems well adapted for application to the future Solar Orbiter mission planned by the ESA where thermal problems are expected to be severe. This type of optical arrangements also provide more flexibility for the optimal selection of performances.
SONTRAC: an imaging spectrometer for solar neutrons
James M. Ryan, Laurent Desorgher, Erwin O. Flueckiger, et al.
An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics-as well as environmental monitoring and medical/radiological sciences. The SONTRAC (SOlar Neutron TRACking) instrument is designed to operate in the neutron energy range of 20-250 MeV. The measurement principle is based on non-relativistic double scatter of neutrons off ambient protons (n-p scattering) within a block of densely packed scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built using 300 μm (250 μm active) scintillating fibers. The science model consists of a 5×5×5 cm cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains, employing image intensifiers and CCD cameras, allow full 3-dimensional reconstruction of scattered proton particle tracks. We report the results of the science model instrument calibration using 35-65 MeV protons. The proton calibration is the first step toward understanding the instrument response to n-p scatter events. Preliminary results give proton energy resolution of 2% (6%) at 67.5 (35) MeV, and angular resolution of 2° (4.5°) at 67.5 (35) MeV. These measurements are being used to validate detailed instrument simulations that will be used to optimize the instrument design and develop quantitative estimates of science return. Based on the proton calibration, neutron energy and angular resolution for a 10×10×10 cm version of SONTRAC is expected to be ~5% and <10°, respectively, while the efficiency of the detector to double n-p scatter events is approximately 1%. We will also discuss ongoing opto-electronic developmental efforts and concepts for extending the instrument response to lower energies.
Toroidal varied-line-space (TVLS) gratings
It is a particular challenge to develop a stigmatic spectrograph for EUV wavelengths since the very low normal-incidence reflectance of standard materials most often requires that the design be restricted to a single optical element which must simultaneously provide both re-imaging and spectral dispersion. This problem has been solved in the past by the use of toroidal gratings with uniform line-space rulings (TULS). A number of solar EUV spectrographs have been based on such designs, including SOHO/CDS, Solar-B/EIS, and the sounding rockets SERTS and EUNIS. More recently, Kita, Harada, and collaborators have developed the theory of spherical gratings with varied line-space rulings (SVLS) operated at unity magnification, which have been flown on several astronomical satellite missions. These ideas are now combined into a spectrograph concept that considers varied-line space grooves ruled onto toroidal gratings. Such TVLS designs are found to provide excellent imaging even at very large spectrograph magnifications and beam-speeds, permitting extremely high-quality performance in remarkably compact instrument packages. Optical characteristics of two solar spectrographs based on this concept are described: SUMI, proposed as a sounding rocket experiment, and NEXUS, proposed for the Solar Dynamics Observatory mission.
Poster Session
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Creation of the permanent space patrol of ionizing solar radiation
Sergey V. Avakyan, Evgenii P. Andreev, Il'ia M. Afanas'ev, et al.
One of the gaps of the modern solar-terrestrial physics is an absence of the permanent space monitoring of the soft X-ray and extreme ultraviolet radiation from the full disk of Sun. The permanent Solar Patrol at the main part of the ionizing radiation spectra 0.8-115 (119) nm does not exist. These measurements are very complicated because of the technical and methodological difficulties. In S.I. Vavilov State Optical Institute (SOI) the apparatus for the Space Solar Patrol (SSP) has been developed in the period 1996-2002 years which includes multiyear experience of developing such apparatus. The base of this apparatus is the use of unique detectors of ionizing radiation the open secondary electron multipliers, which are “solar blind” to near UV, visible and IR radiations of the Sun, and new methodology of these solar spectrophotometric absolute measurements. There are plans to launch the optical electronic apparatus (OEA) of SSP at the Russian Segment of the International Space Station for experimental operation. The paper presents results on the methodology, creating and laboratory testing of the apparatus for Space Solar Patrol Mission.
Electric hardware system design for the Space Solar Telescope
Caihong Sun, Lihong Geng, Shengzheng Jin, et al.
The Space Solar Telescope (SST) is being researched, developed and manufactured by National Astronomical Observatories, Chinese Academy of Sciences (NAOC) in China. It is designed for further solar physics research. There are five payloads with different observation modes on SST, including a Main Optical Telescope (MOT) with 1-meter diameter. Two of five payloads have simple and one-dimension data format, while the others are CCD imaging telescopes. There are 16 CCDs with different resolutions on SST. The total data amount is about 50GB per day. So, onboard electric hardware system is very complex. The whole system is divided into three levels. The top level is for the spacecraft housekeeping, including attitude, thermal, power, and TC/TM etc. control units. The middle level is to manage the five payloads. And the bottom level includes the Scientific Data Processing Unit (SDPU), which will be used to process the original data. 1553B bus and RS-422 bus will take the responsibility for transmitting information between the three levels. The electric hardware system should satisfy the demands of different observation modes and different data formats. In this paper, the hardware system design methods are discussed in detail.
Space Missions and Instrumentation II
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Lightweight Cesic mirrors and their applications
Ceramics technologies were successfully applied to a series of lightweight mirrors with different sizes and requirements. Several joining and optical surface optimizations were applied. Besides the classical rib-structured mirrors also the application of sandwich mirrors with Cesic foam and/or honeycomb structures are going to be tested. For all processes relatively simple straightforward processes can be applied which keeps the products relatively cost-effective.
Space Missions and Instrumentation III
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The reconnection and microscale (RAM) solar-terrestrial probe
Jay A. Bookbinder, Edward DeLuca, Peter Cheimets, et al.
A hot, magnetized plasma such as the solar corona has the property that much of the physics governing its activity takes place on remarkably small spatial and temporal scales, while the response to this activity occurs on large scales. Observations from SMM, TRACE, SOHO and Yohkoh have shown that typical solar active regions have loops ranging in temperature from 0.5 to 10 MK, and flares up to 40MK. The spatial and temporal domains involved have been heretofore inaccessible to direct observations from Earth, so that theory has relied heavily on extrapolations from more accessible regimes, and on speculation. The RAM Solar-Terrestrial Probe consists of a set of carefully selected imaging and spectroscopic instruments that enable definitive studies of the dynamics and energetics of the solar corona.
Why do we need high-resolution observations of the sun?
To make progress on major unsolved problems in solar physics (e.g., coronal heating, eruptive flare/CME initiation, solar wind initiation), we must observe on scales relevant to the underlying physical processes and their signatures. In this review I discuss the factors determining the structure of magnetic fields and plasmas in the Sun’s outer atmosphere, the key observable signatures of the relevant processes and properties, and the instrumental capabilities necessary to detect and measure these signatures. The primary emphasis is on state-of-the-art theoretical and numerical predictions, which often are the only means by which we can estimate the complex time-dependent evolution of the underlying physical mechanisms and their local and global effects on the corona.
Advanced solar imaging from the GOES R spacecraft
Steve Hill, Victor J. Pizzo
The NOAA Space Environment Center is proposing enhanced real-time solar observations to be conducted aboard the GOES satellites in the next decade. These spacecraft are in geosynchronous orbit and offer a convenient platform for near-continuous, high data rate monitoring of the Sun and the interplanetary environment. The instrument complement being considered includes at least two solar imagers: 1) an advanced soft X-ray telescope featuring selectable spectral bandpass, large dynamic range, and high image cadence; and 2) a white light coronagraph with moderate resolution and a field of view sufficient to capture events of geophysical significance. Used in combination with other observational assets, this instrumentation would make a significant improvement in space weather forecast capabilities.
Space Missions and Instrumentation II
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New UV detectors for solar observations
BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the development of novel imaging detectors for UV solar observations. It relies on the properties of wide bandgap materials (in particular diamond and Al-Ga-nitrides). The investigation is proposed in view of the Solar Orbiter (S.O.) UV instruments, for which the expected benefits of the new sensors -primarily visible blindness and radiation hardness- will be highly valuable. Despite various advances in the technology of imaging detectors over the last decades, the present UV imagers based on silicon CCDs or microchannel plates exhibit limitations inherent to their actual material and technology. Yet, the utmost spatial resolution, fast temporal cadence, sensitivity, and photometric accuracy will be decisive for the forthcoming solar space missions. The advent of imagers based on wide-bandgap materials will permit new observations and, by simplifying their design, cheaper instruments. As for the Solar Orbiter, the aspiration for wide-bandgap material (WBGM) based UV detectors is still more sensible because the spacecraft will approach the Sun where the heat and the radiation fluxes are high. We describe the motivations, and present the program to achieve revolutionary flight cameras within the Solar Orbiter schedule as well as relevant UV measurements.
Space Missions and Instrumentation III
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The solar high-resolution imager: coronagraph LYOT mission
Jean-Claude Vial, Xueyan Song, Philippe Lemaire, et al.
The LYOT (LYman Orbiting Telescope) solar mission is proposed to be implemented on a micro-satellite of CNES (France) under phase A study. It includes two main instruments, which image the solar disk and the low corona up to 2.5 Ro in the H I Lyman-α line at 121.6 nm. The spatial resolution is about 1” for the disk and 2.5” for corona. It also carries an EIT-type telescope in the He II (30.4 nm) line. The coronagraph needs a super polished mirror at the entrance pupil to minimize the light scattering. Gratings and optical filters are used to select the Lyman-α wavelength. VUV cameras with 2048×2048 pixels record solar images up to every 10 seconds. The satellite operates at a high telemetry rate (more then 100 kb/s, after onboard data compression). The envisaged orbits are either geostationary or heliosynchronous. Possible launch dates could be end of 2006 - beginning of 2007.
Poster Session
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Analysis on the precision of the correlation tracker in Space Solar Telescope (SST)
Keliang Hu, Yuanyong Deng, Qian Song
The first astronomical space telescope of China, the Space Solar Telescope (SST), of which the main optical telescope's diameter is one meter, is now being built in the National Astronomical Observatories, Chinese Academy of Sciences (NAOC). In order to obtain high precision data of solar magnetic field, long time exposure is required. Therefore, the correlation tracker technology is applied to keep the images stable during the long exposure and to ensure a high spatial resolution. In this paper, we will analyze the accuracy of the correlation tracker of SST by simulating the high-resolution ground-based observations. By our analyses, it is found that at the spatial scale of 0.1", an accuracy of about 0.3-pixel can be achieved when using cross-correlation method together with 25-point parabolic fitting. The result is better than using only cross-correlation method. And after the quantification effect being computed, Our preliminary result shows that it will get similar result by using either higher or lower level quantification. That is, precision acquired by using 16bit quantification cannot reach much higher than by 1bit in the SST/CT.
Evaluation for the displacement damage on CCD caused by high-energy protons
In order to evaluate the radiation shielding efficiency on proton displacement damage for the CCDs that will be boarded space solar telescope project (SST) of China, based on the work of Janesick et. al's, a method is developed to get the stable defects produced by the incident protons. Then the proton caused degradation of the CCD specifications of charge transfer efficiency (CTE) and bulk dark current generation is calculated for SST after its 3-years-long mission on orbit and a 3mm thick aluminum shield is suggested for the CCDs of the mission. The method is a new attempt to predict the displacement-induced CTI and dark current together.
High-order adaptive optical system for big bear solar observatory
Leonid V. Didkovsky, Alexander Dolgushyn, William Marquette, et al.
We present a high-order adaptive optical system for the 26-inch vacuum solar telescope of Big Bear Solar Observatory. A small elliptical tip/tilt mirror is installed at the end of the existing coude optical path on the fast two-axis tip/tilt platform with its resonant frequency around 3.3 kHz. A 77 mm diameter deformable mirror with 76 subapertures as well as wave-front sensors (correlation tracker and Shack-Hartman) and scientific channels for visible and IR polarimetry are installed on an optical table. The correlation tracker sensor can detect differences at 2 kHz between a 32×32 reference frame and real time frames. The WFS channel detects 2.5 kHz (in binned mode) high-order wave-front atmosphere aberrations to improve solar images for two imaging magnetographs based on Fabry-Perot etalons in telecentric configurations. The imaging magnetograph channels may work simultaneously in a visible and IR spectral windows with FOVs of about 180×180 arc sec, spatial resolution of about 0.2 arc sec/pixel and SNR of about 400 and 600 accordingly for 0.25 sec integration time.
Ground Based Telescopes and Instruments II
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GREGOR: the new 1.5-m solar telescope on Tenerife
Reiner Volkmer, Oskar von der Luehe, Franz Kneer, et al.
The new 1.5 m high resolution telescope will be build up on the reused solar tower of the German 45 cm Gregory Coude Telescope at the Teide Observatory, Izana, Tenerife. The new telescope is a Gregory type with open telescope structure, alt-azimuth mount, complete retractable dome, and a pool of well established and new developed post focus instruments. An adaptive optics system provides the capability for diffraction limited observations at visible wavelengths and the polarimetry device in the secondary focus reduces the perturbation due to instrumental polarization in an efficient way. We describe the main optical characteristics and the focal plane instrumentation with respect to the latest status of the project.
Poster Session
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Automated image standardization of the synoptic solar observations at the Meudon observatory
Stan S. Ipson, Valentin Zharkova, Ali Khalil Benkhalil, et al.
The robust techniques developed to put the synoptic solar images into a standardized form of a 'virtual solar image' are presented. The techniques include limb fitting, removal of geometrical distortion, centre position and size standardization and intensity normalization. The limb fitting starts with an initial estimate of the solar centre using raw 12-bit image data and then applies a Canny edge-detection routine. Candidate edge points for the limb are selected using a voting method and the chosen points fitted to a quadratic function by minimizing the algebraic distance using SVD. The five parameters of the ellipse fitting the limb are extracted from the quadratic function. Together with knowledge of cause of the geometrical distortion these parameters are used to define an affine transformation that corrects the image shape. Corrected images are generated using the nearest neighbor, bilinear or bicubic interpolation. Intensity renormalization is also required because of a limb darkening and variation in the atmosphere visibility over the solar disc. It is achieved by fitting a background function in polar co-ordinates to a set of sample points having the median intensities and by standardizing the average brightness. Representative examples of intermediate and final processed results are presented in addition to the algorithms developed. The techniques were also applied to the some images taken from BBSO, Kanzelhoehe and Kiepenheuer Institution observatories. The research is done for the European Grid of Solar Observations (EGSO) project, IST-2001-32409.
Polarimetry of the Solar Atmosphere I
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KAOS: adaptive optics system for the Vacuum Tower Telescope at Teide Observatory
Oskar van der Luehe, Dirk Soltau, Thomas Berkefeld, et al.
We are completing the integration of a solar adaptive optics system KAOS at the 70 cm diameter Vacuum Tower telescope (VTT) on Tenerife. The system is capable to compensate some 30 modes of wavefront aberration with closed-loop bandwidth of about 100 Hz anywhere on the solar disk. We describe the design goals, the main characteristics of KAOS and present a first demonstration of its performance.