Proceedings Volume 7440

Techniques and Instrumentation for Detection of Exoplanets IV

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Proceedings Volume 7440

Techniques and Instrumentation for Detection of Exoplanets IV

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Volume Details

Date Published: 20 August 2009
Contents: 7 Sessions, 44 Papers, 0 Presentations
Conference: SPIE Optical Engineering + Applications 2009
Volume Number: 7440

Table of Contents

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Table of Contents

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  • Coronagraph Design, Nullers, and Transits
  • External Occulters
  • Wavefront Correction and Pupil Remapping
  • Ground-based Spectroscopy
  • Ground-based Direct Detection
  • Performance Modeling
  • Coronagraph Design, Nullers, and Transits
  • Poster Session
Coronagraph Design, Nullers, and Transits
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In Memoriam: Russ Makidon
This PDF file contains the front matter associated with SPIE Proceedings Volume 7440, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing
External Occulters
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Terrestrial Planet Finder: coda to 10 years of technology development
The Terrestrial Planet Finder (TPF) was proposed as a mission concept to the 2000 Decadal Survey, and received a very high ranking amongst the major initiatives that were then reviewed. As proposed, it was a formationflying array of four 3.5-m class mid-infrared telescopes, linked together as an interferometer. Its science goal was to survey approximately 150 nearby stars for the presence of Earth-like planets, to detect signs of life or habitability, and to enable revolutionary advances in high angular resolution astrophysics. The Decadal Survey Committee recommended that $200M be invested to advance TPF technology development in the Decade of 2000-2010. This paper presents the results of NASA's investment.
Starlight suppression from the starshade testbed at NGAS
Rocco Samuele, Tiffany Glassman, Adam M. J. Johnson, et al.
We report on progress at the Northrop Grumman Aerospace Systems (NGAS) starshade testbed. The starshade testbed is a 42.8 m, vacuum chamber designed to replicate the Fresnel number of an equivalent full-scale starshade mission, namely the flagship New Worlds Observer (NWO) configuration. Subscale starshades manufactured by the NGAS foundry have shown 10-7 starlight suppression at an equivalent full-mission inner working angle of 85 milliarseconds. In this paper, we present an overview of the experimental set up, scaling relationships to an equivalent full-scale mission, and preliminary results from the testbed. We also discuss potential limitations of the current generation of starshades and improvements for the future.
Occulter design for THEIA
An occulter is an instrument designed to suppress starlight by diffraction from its edges; most are designed to be circular, with a set of identical "petals" running around the outside. Proposed space-based occulters are lightweight, deployed screens tens of meters in diameter with challenging accuracy requirements. In this paper we describe the design of an occulter for the THEIA mission concept. THEIA consists of a 4-meter telescope diffraction limited to 300 nm, and a 40-meter external occulter to provide high-contrast imaging. Operating from 250 to 1000 nm, it will provide a rich family of science projects, including exoplanet characterization, ultraviolet spectroscopy, and very wide-field imaging. Originally conceived of as a hybrid system employing both an occulter and internal coronagraph, THEIA now uses a single occulter to achieve all of the starlight suppression but at two different distances from the telescope in order to minimize size and distance. We describe the basic design principles of the THEIA occulter, its final configuration, performance, and sensitivity.
Progress on the occulter experiment at Princeton
Eric Cady, Kunjithapatham Balasubramanian, Michael Carr, et al.
An occulter is used in conjunction with a separate telescope to suppress the light of a distant star. To demonstrate the performance of this system, we are building an occulter experiment in the laboratory at Princeton. This experiment will use an etched silicon mask as the occulter, with some modifications to try to improve the performance. The occulter is illuminated by a diverging laser beam to reduce the aberrations from the optics before the occulter. We present the progress of this experiment and expectations for future work.
A method for modifying occulter shapes
An occulter is an instrument designed to suppress starlight by diffraction from its edges; most are designed to be circular, with a set of identical "petals" running around the outside. Proposed space-based occulters are lightweight, deployed screens tens of meters in diameter with challenging accuracy requirements. We describe a general method for modifying the shape of an occulter to accommodate engineering considerations and show how to calculate the resulting wavefront. This method can be used to place hinges and tensioning elements between petals, to reduce tolerancing requirements by allowing gaps between petals to be moved elsewhere, and to potentially reduce the number of petals required on an occulter.
Analysis of external occulters in the presence of defects
Fifty meter-class external occulters have been proposed to detect earth-like planets. The THEIA concept1, a forty-meter diameter occulter with twenty ten-meter petals has the necessary nominal performance to achieve this goal. This paper examines whether this design is robust against expected manufacturing and deployment errors. The development of a numerical algorithm that represents the mask defects as a collection of rectangular apertures mitigates the problems associated with modeling diffraction phenomena produced by an occulter with characteristic physical dimensions that span five orders of magnitude. The field from each of these rectangles, which is proportional to a two-dimensional sinc function at the telescope, is added to the diffracted field from the nominal occulter. Results for a set of representative defects are presented. A single-petal, single-defect error budget, based on a minimum contrast of 10-12 at 75 or 118 milli-arcseconds from the host star from 0.3 μ to 0.9 μ, is quoted. A Monte Carlo-type simulation that predicts the performance of the occulter in the presence of random combinations of all of the error demonstrates that the system contrast can maintained to better than 10-11 from 0.3 μ to 0.9 μ if the values in the error budget can be achieved.
Results from the automated Design Reference Mission constructor for exoplanet imagers
We use our automated Design Reference Mission construction framework to evaluate the performance of multiple direct exoplanet imager mission concepts on a variety of metrics including: total number of planetary detections, number of unique planets found, number of target stars observed and number of successful spectral characterizations. We evaluate designs of self-contained coronagraphs and co-orbiting occulters. Performance is evaluated on simulated universes with differing frequencies of planets and varying expected occurrence rates of different planet types.
A starshade for JWST: science goals and optimization
The James Webb Space Telescope will be an extraordinary observatory, providing a huge range of exciting new astrophysical results. However, by itself it will not be capable of directly imaging planets in the habitable zone of nearby stars, one of the most fascinating goals of astronomy for the coming decade. In this paper we discuss the New Worlds Probe (NWP) concept whereby we use an external occulter (or starshade) to cast a shadow from the star onto the telescope, therefore canceling the direct star light while the light from a planet is not affected. This concept enables JWST to take images and spectra of extrasolar planets with sufficient contrast and inner working angle to be able to discover planets down to the size of the Earth in the habitable zone around nearby stars. JWST's instruments are appropriate to achieve low resolution spectroscopy (R ≅ 40) of these planets, and address a series of fundamental questions: are there planets in the habitable zone around nearby stars? What is the composition of their atmosphere? What are the brightness and structures of exozodiacal disks around nearby stars? What is the mass and composition of currently known giant planets? In this paper we study the starshade optimization for JWST given the instrumental constraints, and show that the modest optical quality of the telescope at short wavelength does not impact the possibility of using a starshade. We propose a solution to enable imaging and spectroscopy using target acquisition filters. We discuss possible time allocation among science goals based on exposure time estimates and total available observing time. The starshade can be launched up to 3 years after JWST and rendezvous with the telescope in orbit around L2.
The utility of astrometry as a precursor to direct detection
A recent source of debate in the exoplanet community has been the question of whether an astrometry 'precursor' mission is required in order for a direct detection mission to succeed. Using an existing framework for the evaluation of direct detection missions, we address this question by incorporating data which may be generated by an astrometry mission. We present results for cases where the astrometry mission is able to resolve which target stars have planets, where it is able to fit a subset of the orbital parameters of discovered planets, and where the astrometric data is good enough to fit complete orbits. Each of these is evaluated assuming perfect performance on the part of the astrometric instrument, and with varying levels of error.
Wavefront Correction and Pupil Remapping
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Two-camera wavefront estimation with a Gercheberg-Saxton based scheme
Most mature wavefront-estimation algorithms for high-contrast imaging rely on a-priori knowledge of the deformable mirror (DM) surface and thus are limited by uncertainty in the physics of the DM. In this paper, we review the DM diversity wavefront estimation algorithm and introduce a DM-independent method of wavefront estimation that utilizes two cameras and a Gerchberg-Saxton-based iterative phase retrieval scheme. We compare the two estimation algorithms, and we present the creation of a dark hole in the image plane using the Stroke Minimization correction algorithm and this two-camera estimation.
A unified formailism for high contrast imaging correction algorithms
This paper introduces a unified formulism to describe many of the high contrast correction methods, namely, phase conjugation, classical speckle nulling and energy minimization. This unified formalism led to the Electric Field Conjugation (EFC) algorithm where the solution found is such that minimizes the sum of the estimated electric field at a desired plane and the electric field due to the corrective elements in the system. Applying this formalism led to the conclusion that all the other methods are special cases of EFC.
Numerical propagator through PIAA optics
In this communication we address two outstanding issues pertaining the modeling of PIAA coronagraphs, accurate numerical propagation of edge effects and fast propagation of mid spatial frequencies for wavefront control. In order to solve them, we first derive a quadratic approximation of the Huygens wavelets that allows us to develop an angular spectrum propagator for pupil remapping. Using this result we introduce an independent method to verify the ultimate contrast floor, due to edge propagation effects, of PIAA units currently being tested in various testbeds. We then delve into the details of a novel fast algorithm, based on the recognition that angular spectrum computations with a pre-apodised system are computationally light. When used for the propagation of mid spatial frequencies, such a fast propagator will ultimately allow us to develop robust wavefront control algorithms with DMs located before the pupil remapping mirrors.
Detecting and characterizing exoplanets with a 1.4-m space telescope: the Pupil mapping Exoplanet Coronagraphic Observer (PECO)
Olivier Guyon, James R. P. Angel, Ruslan Belikov, et al.
The Pupil-mapping Exoplanet Coronagraphic Observer (PECO) mission concept uses a coronagraphic 1.4-m space-based telescope to both image and characterize extra-solar planetary systems at optical wavelengths. PECO delivers 10-10 contrast at 2 λ/D separation (0.15") using a high-performance Phase-Induced Amplitude Apodization (PIAA) coronagraph which remaps the telescope pupil and uses nearly all of the light coming into the aperture. For exoplanet characterization, PECO acquires narrow field images simultaneously in 16 spectral bands over wavelengths from 0.4 to 0.9 μm, utilizing all available photons for maximum wavefront sensing and sensitivity for imaging and spectroscopy. The optical design is optimized for simultaneous low-resolution spectral characterization of both planets and dust disks using a moderate-sized telescope. PECO will image the habitable zones of about 20 known F, G, K stars at a spectral resolution of R≈15 with sensitivity sufficient to detect and characterize Earth-like planets and to map dust disks to within a fraction of our own zodiacal dust cloud brightness. The PIAA coronagraph adopted for PECO reduces the required telescope diameter by a factor of two compared with other coronagraph approaches that were considered for Terrestrial Planet Finder Coronagraph Flight Baseline 1, and would therefore also be highly valuable for larger telescope diameters. We report on ongoing laboratory activities to develop and mature key PECO technologies, as well as detailed analysis aimed at verifying PECO's wavefront and pointing stability requirement can be met without requiring development of new technologies.
Science performance of the Pupil-mapping Exoplanet Coronagraphic Observer (PECO)
The Pupil-mapping Exoplanet Coronagraphic Observer (PECO) medium-class mission concept is a 1.4-m space-based optical telescope with a high-performance Phase-Induced Amplitude Apodization (PIAA) coronagraph. PECO detects and characterizes exoplanets and their host systems at 2 λ/D (0.15") separation at high contrast (~1e-10). The optical design images in 16 filter bands from 400-800 nm, producing simultaneous low-resolution target spectra. PECO will characterize terrestrial planets in the habitable zones of ~20 nearby F, G, K stars at spectral resolution of R~15, as well as over a dozen radial-velocity planets and over a hundred gas giants and exozodiacal dust disks. We discuss PECO's expected science performance and simulated data products over its three-year mission lifetime.
Phase-induced amplitude apodization (PIAA) coronagraph testing at the High Contrast Imaging Testbed
We present the current status of our testing of a phase-induced amplitude apodization (PIAA) coronagraph at the Jet Propulsion Lab's High Contrast Imaging Testbed (HCIT) vacuum facilities. These PIAA optics were designed to produce a point-spread function containing a region whose intensity is below 10-9 over a 20-percent fractional bandpass, comparable to the requirements for direct imaging of exoplanets from space. The results presented here show contrast levels of 4×10-7 in monochromatic light, with an inner working angle of 2.4 λ/D. The instrumentation is described here, as well as the testing procedures, wavefront control, and results.
Performance sensitivity studies on the PIAA implementation of the High Contrast Imaging Testbed
We have investigated the dependence of the High Contrast Imaging Testbed (HCIT) Phase Induced Amplitude Apodization (PIAA) coronagraph system performance on the rigid-body perturbations of various optics. The structural design of the optical system as well as the parameters of various optical elements used in the analysis are drawn from those of the PIAA/HCIT system that have been and will be implemented, and the simulation takes into account the surface errors of various optics. In this paper, we report our findings when the input light is a narrowband beam.
First results on a new PIAA coronagraph testbed at NASA Ames
Ruslan Belikov, Eugene Pluzhnik, Michael S. Connelley, et al.
Direct imaging of extrasolar planets, and Earth-like planets in particular, is an exciting but difficult problem requiring a telescope imaging system with 1010 contrast at separations of 100mas and less. Furthermore, the current NASA science budget may only allow for a small 1-2m space telescope for this task, which puts strong demands on the performance of the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA) coronagraph has been maturing and may enable Earth-like planet imaging for such small telescopes. In this paper, we report on the latest results from a new testbed at NASA Ames focused on testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to complement existing efforts at NASA JPL. For our wavefront control we are focusing on using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. At time of this writing, we are operating a refractive PIAA system and have achieved contrasts of about 1.2x10-7 in a dark zone from 2.0 to 4.8 λ/D (with 6.6x10-8 in selected regions). In this paper, we present these results, describe our methods, present an analysis of current limiting factors, and solutions to overcome them.
Ground-based Spectroscopy
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A new generation multi-object Doppler instrument for the SDSS-III Multi-object APO Radial Velocity Exoplanet Large-area Survey
Jian Ge, Brian Lee, Nathan De Lee, et al.
We report performance of a new generation multi-object Doppler instrument for the on-going Multi-object APO Radial-velocity Exoplanet Large-area Survey (MARVELS) of the Sloan Digital Sky Survey III (SDSS-III) program. This instrument is based on dispersed fixed-delay interferomtry design. It consists of a multi-object fiber-feed, a thermally compensated monolithic fixed-delay interferometer, a high throughput spectrograph and a 4kx4k CCD camera. The spectrograph resolving power is R=11,000 and the wavelength coverage is 500-570 nm. The instrument is capable of measuring 60 stars in a single exposure for high to moderate precision radial velocity (3-20 m/s) measurements depending on the star magnitudes (V=7.6-12). The instrument was commissioned at the SDSS telescope in September 2008 and used to collect science data starting in October 2008. Observations of reference stars show that the measured photon noise limiting errors are consistent with the prediction for most of the measurements.
Calibration of high accuracy radial velocity spectrographs: beyond the Th-Ar lamps
Since its first light in 2003, the HARPS radial velocity spectrograph (RVS) has performed exquisitely well on the 3.6m ESO telescope at La Silla Observatory (Chile). It now routinely exhibits a measurement noise of 0.5 m/s or 1.7 10-9 on a relative scale. Despite innovative work by Lovis and colleagues [14] to improve the accuracy obtained with the calibration lamps used, there is evidence that still better performance could be achieved by using more stable wavelength standards. In this paper, we present two methods are aim at overcoming the shortcoming of present day calibrators and that could satisfy the need for a cm/s -level calibrator like we are planning on using on the 2nd generation instruments at the VLT and on the ELT instrumentation. A temperature-stabilized Fabry-Perot interferometer has the promise of being stable to a few cm/s and has very uniform line levels and spacings, while a laser comb has already achieved a precision better than 15 cm/s, despite using only one of the 72 orders of the spectrographs.
Ground-based Direct Detection
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The Subaru Coronagraphic Extreme-AO Project
Frantz Martinache, Olivier Guyon
The Subaru Coronagraphic Extreme AO (SCExAO) Project is an upgrade to the newly commissioned coronagraphic imager HiCIAO for the Subaru Telescope, in the context of a massive survey for exoplanets and disks called SEEDS. SCExAO combines a high-performance coronagraph PIAA coronagraph and non-redundant aperture masking interferometry to a MEMS-based wavefront control system to be used in addition to the 188- actuator Subaru Adaptive Optics (AO188) system. The upgrade is designed as a flexible platform with easy access to both pupil and image planes to allow quick implementation of new high-angular resolution techniques, using a combination of interferometry and coronagraphy. The SCExAO system will enhance SEEDS by offering access to smaller separations and improved PSF calibration, and will therefore allow high quality follow-up observations of challenging SEEDS candidates. SCExAO will also enable new science investigations requiring high contrast imaging of the innermost (< 0.2 arc second) surrounding of stars.
SPHERE: the VLT planet imager in the post FDR phase
SPHERE, the ESO extra-solar planet imager for the VLT is aimed at the direct detection and spectral characterization of extra-solar planets. Its whole design is optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star. SPHERE has passed its Final Design Review (FDR) in December 2008 and it is in the manufacturing and integration phase. We review the most challenging specifications and expected performance of this instrument; then we present the latest stage of the design chosen to meet the specifications, the progress in the manufacturing as well as the integration and test strategy to insure gradual verification of performances at all levels.
Calibrating SPHERE, the exo-planet imager for the VLT
Francois Wildi, David Mouillet, Jean-Luc Beuzit, et al.
One of the main challenges to obtain the contrast of >15mag targeted by an extra-solar planet imager like SPHERE lies in the calibration of all the different elements participating in the final performance. Starting with the calibration of the AO system and its three embedded loops, the calibration of the non-common path aberrations, the calibration of the NIR dual band imager, the NIR integral field spectrograph, the NIR spectrograph, the visible high accuracy polarimeter and the visible imager all require sophisticated calibration procedures. The calibration process requires a specific extensive calibration unit that provides the different sources across the spectrum (500-2320nm) with the stabilities and precisions required. This article addresses the challenges met by the hardware and the instrument software used for the calibration of SPHERE.
The Gemini Planet Imager coronagraph testbed
The Gemini Planet Imager (GPI) is a new facility instrument to be commissioned at the 8-m Gemini South telescope in early 2011. It combines of several subsystems including a 1500 subaperture Extreme Adaptive Optics system, an Apodized Pupil Lyot Coronagraph, a near-infrared high-accuracy interferometric wavefront sensor, and an Integral Field Unit Spectrograph, which serves as the science instrument. GPI's main scientific goal is to detect and characterize relatively young (<2GYr), self luminous planets with planet-star brightness ratios of ≤ 10-7 in the near infrared. Here we present an overview of the coronagraph subsystem, which includes a pupil apodization, a hard-edged focal plane mask and a Lyot stop. We discuss designs optimization, masks fabrication and testing. We describe a near infrared testbed, which achieved broadband contrast (H-band) below 10-6 at separations > 5λ/D, without active wavefront control (no deformable mirror). We use Fresnel propagation modeling to analyze the testbed results.
The Gemini Planet Imager calibration testbed
J. Kent Wallace, Rick Burruss, Laurent Pueyo, et al.
The calibration wavefront system for GPI will measure the complex wavefront at the apodized pupil and provide slow phase corrections to the AO system to mitigate against errors that would cause a loss in contrast. This talk describes both the low-order and high-order sensors in the calibration wavefront sensor and how the information is combined to form the wavefront estimate before the coronagraph. Expected performance for this wavefront sensor will also be described for typical observing scenarios. Finally, we will show labratory results from our calibration testbed that demonstrate the instrument performance at levels commensurate with those required on the GPI instrument.
Performance Modeling
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Stellar coronagraph performance impact due to particulate contamination and scatter
The detection and characterization of earth-like exo-planets with space coronagraph instruments could be adversely affected by contamination of the many optical surfaces from the telescope primary mirror to the coronagraph mask. Particulate contamination that may accumulate even in clean room conditions over the period of integration, testing, and launch can cause performance degradation due to both coherent and incoherent scatter. While the coherent components can be compensated in broad-band light using a sequential deformable mirror architecture, incoherent scatter would remain. We show the challenges and effects of particulate contamination based on measurements and estimates, and discuss the requirements throughout the coronagraph system while accounting for the wavefront control system.
Thermo/opto/mechanical analysis of large apertures for exoplanet detection using Cielo
Elizabeth O. Jordan, Mike Chainyk, Feras Habbal, et al.
The next generation of space telescopes will be designed to meet increasingly challenging science goals. The operating environment and required precision of these telescopes will make complete verification via ground tests impossible, and will place a greater reliance on numerical simulation. The current state of the art in thermal, mechanical and optical modeling involves three disparate computational models, several analysis codes and tools to transition results between these models. However, the active controls necessary to meet the next generation of requirements for space telescopes will require integrated thermal, structural, optical and controls analysis. To meet these challenges, JPL has developed Cielo, an in-house finite element tool capable of multi-physics simulations using a common finite element model, for thermal, structural and optical aberration analysis. In this paper, we will discuss the use of Cielo for analysis of a coronagraph and an occulter designed to observe Earth-like planets around nearby stars. We will compare thermal and structural results from Cielo with results from commercial off the shelf (COTS) tools to verify the new approach. We will perform variations of key parameters to demonstrate how margins and uncertainties can be quantified using the new approach.
A general tool for evaluating high-contrast coronagraphic telescope performance error budgets
This paper describes a general purpose Coronagraph Performance Error Budget (CPEB) tool that we have developed under the NASA Exoplanet Exploration Program. The CPEB automates many of the key steps required to evaluate the scattered starlight contrast in the dark hole of a space-based coronagraph. It operates in 3 steps: first, a CodeV or Zemax prescription is converted into a MACOS optical prescription. Second, a Matlab program calls ray-trace code that generates linear beam-walk and aberration sensitivity matrices for motions of the optical elements and line-ofsight pointing, with and without controlled coarse and fine-steering mirrors. Third, the sensitivity matrices are imported by macros into Excel 2007 where the error budget is created. Once created, the user specifies the quality of each optic from a predefined set of PSDs. The spreadsheet creates a nominal set of thermal and jitter motions and combines them with the sensitivity matrices to generate an error budget for the system. The user can easily modify the motion allocations to perform trade studies.
Coronagraph Design, Nullers, and Transits
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The JWST/NIRCam coronagraph: mask design and fabrication
The NIRCam instrument on the James Webb Space Telescope will provide coronagraphic imaging from λ =1-5 μm of high contrast sources such as extrasolar planets and circumstellar disks. A Lyot coronagraph with a variety of circular and wedge-shaped occulting masks and matching Lyot pupil stops will be implemented. The occulters approximate grayscale transmission profiles using halftone binary patterns comprising wavelength-sized metal dots on anti-reflection coated sapphire substrates. The mask patterns are being created in the Micro Devices Laboratory at the Jet Propulsion Laboratory using electron beam lithography. Samples of these occulters have been successfully evaluated in a coronagraphic testbed. In a separate process, the complex apertures that form the Lyot stops will be deposited onto optical wedges. The NIRCam coronagraph flight components are expected to be completed this year.
Vector vortex coronagraph: first results in the visible
Dimitri Mawet, John T. Trauger, Eugene Serabyn, et al.
We report the status of JPL and JDSU ongoing technological developments and contrast results of the vector vortex coronagraph (VVC) made out of liquid crystal polymers (LCP). The first topological charge 4 VVC was tested on the high contrast imaging testbed (HCIT) around 800 nm, under vacuum and with active wavefront control (32x32 Xinetics deformable mirror). We measured the inner working angle or IWA (50% off-axis transmission) at ~ 1.8λ/d. A one-sided dark hole ranging from 3λ/d to 10λ/d was created in polarized light, showing a mean contrast of ~ 2 × 10-7 over a 10% bandwidth. This contrast was maintained very close in (3 λ/d) in a reduced 2% bandwidth. These tests begin to demonstrate the potential of the LCP technology in the most demanding application of a space-based telescope dedicated to extrasolar planet characterization. The main limitations were identified as coming from incoherent sources such as multiple reflections, and residual chromaticity. A second generation of improved masks tackling these issues is being manufactured and will be tested on the HCIT in the coming months.
Planetary system and star formation science with non-redundant masking on JWST
Non-redundant masking (NRM) is a high contrast high resolution technique that is relevant for future space missions dedicated to either general astrophysics or extrasolar planetary astronomy. NRM mitigates not only atmospheric but instrument-induced speckle noise as well. The recently added mask in the Fine Guidance Sensor Tunable Filter Imager (FGS-TFI) on the James Webb Space Telescope (JWST) will open up a search space between 50 and 400 mas at wavelengths longer than 3.8μm. Contrast of 104 will be achievable in a 10 ks exposure of an M = 7 star, with routine observing, target acquisition, and data calibration methods. NRM places protoplanets in Taurus as well as Jovians younger than 300Myr and more massive than 2MJ orbiting solar type stars within JWST's reach. Stars as bright as M = 3 will also be observable, thus meshing well with next-generation ground-based extreme adaptive optics coronagraphs. This parameter space is inaccessible to both JWST coronagraphs and future 30-m class ground-based telescopes, especially in the mid-IR. We show that NRM used on future space telescopes can deliver unsurpassed image contrast in key niches, while reducing mission risk associated with active primary mirrors.
Current status of the assessment of the ESA Cosmic Vision mission candidate PLATO
R. Lindberg, A. Stankov, M. Fridlund, et al.
PLATO is a candidate of the European Space Agency's Science programme Cosmic Vision 2015-2025. "PLAnetary Transits and Oscillations of stars" aims to characterise exoplanetary systems by detecting planetary transits and conducting asteroseismology of their parent stars. This is achieved through high-precision photometry (visible waveband). PLATO is currently in assessment phase, which was started with an internal study in ESA's Concurrent Design Facility (CDF). Two phase-A, parallel industrial studies with 12-months durations are being conducted until July 2009. The objectives of these studies are to understand the critical areas inherent to this mission and assess the trade-offs in order to define a baseline concept that optimises scientific return while minimising complexity and risk and meeting the applicable programmatic constraints. PLATO will operate in a large-amplitude orbit around Sun-Earth L2 where it will observe targets for several years in order to characterise the exoplanetary transits. To observe enough stars (with focus on Sun-like cool dwarfs) to maximize the number of transit detections, a large field-of-view (FoV) is required as well as a sufficiently high collecting area. PLATO will achieve this objective by utilizing several smaller telescopes instead of one large telescope. Several different optical designs, both reflective and refractive, are being studied. Due to the large number of simultaneously observed stars the spacecraft will require a high degree of autonomy and adequate on-board processing capability. Moreover, the stars must be monitored with high accuracy, which means that the spacecraft must provide a stable environment in terms of pointing stability and thermal environment. This paper summarises the results of the assessment studies.
Visible nulling coronagraph testbed results
We report on our recent laboratory results with the NASA/Goddard Space Flight Center (GSFC) Visible Nulling Coronagraph (VNC) testbed. We have experimentally achieved focal plane contrasts of 1 x 108 and approaching 109 at inner working angles of 2 * wavelength/D and 4 * wavelength/D respectively where D is the aperture diameter. The result was obtained using a broadband source with a narrowband spectral filter of width 10 nm centered on 630 nm. To date this is the deepest nulling result with a visible nulling coronagraph yet obtained. Developed also is a Null Control Breadboard (NCB) to assess and quantify MEMS based segmented deformable mirror technology and develop and assess closed-loop null sensing and control algorithm performance from both the pupil and focal planes. We have demonstrated closed-loop control at 27 Hz in the laboratory environment. Efforts are underway to first bring the contrast to > 109 necessary for the direct detection and characterization of jovian (Jupiter-like) and then to > 1010 necessary for terrestrial (Earth-like) exosolar planets. Short term advancements are expected to both broaden the spectral passband from 10 nm to 100 nm and to increase both the long-term stability to > 2 hours and the extent of the null out to a ~ 10 * wavelength / D via the use of MEMS based segmented deformable mirror technology, a coherent fiber bundle, achromatic phase shifters, all in a vacuum chamber at the GSFC VNC facility. Additionally an extreme stability textbook sized compact VNC is under development.
Poster Session
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Starshade scaling relations
Tiffany Glassman, Amy S. Lo, Jonathan Arenberg, et al.
The New Worlds Observer enables high-contrast imaging by placing a space telescope in the dark shadow cast by an apodized starshade. Depending on the science requirements, we consider starshades that provide a wide range of contrast (from ~10-4 to more than 10-15) over an octave of wavelength (from UV to Visible) at a variety of inner working angles (from a few milliarcseconds to several arcseconds). The starshade-telescope system is described by many parameters, including starshade diameter, telescope diameter, starshade-telescope separation, and wavelength range, that interact non-linearly. In this paper, we show how the different parameters contribute to the starshade's performance and discuss the selection process for different science requirements.
An evaluation of the effects of non-uniform exo-zodiacal dust distributions on planetary observations
As the push for a dedicated direct exoplanet imaging mission intensifies, and numerous mission concepts are drafted and refined, a growing concern has been that not enough attention has been paid to the effects of exozodiacal light. As most mission simulations have assumed uniform or smoothly varying exozodi levels, there exists a danger that a potential future planet imager will be unable to succeed in its mission due to 'clumped' exozodi. We have used our existing framework for evaluating the capabilities of direct planet imagers to simulate the effects of non-uniform exozodi on mission outcomes, including modeling the increased integration time that may be required, and the possibility of increased false positives.
End-to-end simulations of different coronagraphic techniques
The NASA exoplanet exploration program is dedicated to developing technologies for detecting and characterizing extrasolar planets. In support of that program we have evaluated three different coronagraphic techniques (bandlimited Lyot, optical vortex, and phase-induced pupil apodization) using optical propagation simulations. These utilized a complete hypothetical telescope+coronagraph system with phase and amplitude aberrations. Wavefront control using dual sequential deformable mirrors was performed. We discuss the different computational techniques necessary to accurately simulate each coronagraph.
FIB machining of occulting masks for imaging of extrasolar planets
Shilpa N. Raja, Michael J. Aziz, James W. Foley, et al.
We are developing the ability for Focused Ion Beam (FIB) machining of occulting masks for use in coronagraphs. These masks will be used as soft-edged Lyot stops to suppress light from stars and allow direct imaging of extrasolar planets. The FIB approach is attractive because it has the potential for higher precision than mechanical machining and for larger volumes than electron-beam lithography. The mask fabrication process is trifold: 1) a transparent material-currently, poly(methyl methacrylate) (PMMA)-is doped with dyes; 2) the mask shape is FIB milled into the material; and 3) the mask is coated with another layer of index-matching transparent absorber. Using a Zeiss NVision 40 FIB system, we have fabricated conical-shaped masks of various slopes in dye-doped PMMA. Inherent in this process is the advantage of control of the features through programming the ion beam track. We have also optically characterized these masks as well as the dye-doped absorbing material. We have found that the dye-doped PMMA has a very high absorbance, >1 OD.
Laboratory experiment of a high-contrast imaging coronagraph with new step-transmission filters
We present the latest results of our laboratory experiment of the coronagraph with step-transmission filters. The primary goal of this work is to test the stability of the coronagraph and identify the main factors that limit its performance. At present, a series of step-transmission filters has been designed. These filters were manufactured with Cr film on a glass substrate with a high surface quality. During the process of the experiment of each filter, we have identified several contrast limiting factors, which includes the non-symmetry of the coating film, transmission error, scattered light and the optical aberration caused by the thickness difference of coating film. To eliminate these factors, we developed a procedure for the correct test of the coronagraph and finally it delivered a contrast in the order of 10-6~10-7 at an angular distance of 4λD, which is well consistent with theoretical design. As a follow-up effort, a deformable mirror has been manufactured to correct the wave-front error of the optical system, which should deliver better performance with an extra contrast improvement in the order of 10-2~10-3. It is shown that the step-transmission filter based coronagraph is promising for the high-contrast imaging of earth-like planets.
Balloon exoplanet nulling interferometer (BENI)
We evaluate the feasibility of a balloon-borne nulling interferometer to detect and characterize an exosolar planet and the surrounding debris disk. The existing instrument consists of a three-telescope Fizeau imaging interferometer with thre fast steering mirrors and three delay lines operating at 800 Hz for closed-loop control of wavefront errors and fine pointing. A compact visible nulling interferometer would be coupled to the imaging interferometer and in principle, allows deep starlight suppression. Atmospheric simulations of the environment above 100,000 feet show that balloonborne payloads are a possible path towards the direct detection and characterization of a limited set of exoplanets and debris disks. Furthermore, rapid development of lower cost balloon payloads provide a path towards advancement of NASA technology readiness levels for future space-based exoplanet missions. Discussed are the BENI mission and instrument, the balloon environment and the feasibility of such a balloon-borne mission.
The Monolithic Achromatic Nulling Interference Coronagraph (MANIC) testbed
Brian A. Hicks, Timothy A. Cook, Benjamin F. Lane, et al.
We present progress in the development of the monolithic achromatic nulling interference coronagraph (MANIC), a nulling optic designed to enable direct imaging of nearby Jupiter-like exoplanets. The experimental testbed for measuring the optical path difference (OPD) between the two arms of the nuller and characterizing the nuller's performance is described. The OPD measurement will be used to determine the relative thicknesses of compensator plates needed to complete MANIC's fabrication. Demonstrating the performance of the monolith will include sub-aperture nulling of laser and white-light sources using a single PZT-controlled delay line on one half of a bisected input beam.
Calibrating IR optical densities for the Gemini Planet Imager extreme adaptive optics coronagraph apodizers
High contrast imaging sometimes uses apodized masks in coronagraphs to suppress diffracted starlight from a bright source in order to observe its environs. Continuously graded opacity material and metallic half-tone dots are two possible apodizers fabrication techniques. In the latter approach if dot sizes are comparable to the wavelength of the light, surface plasmon effects can complicate the optical density (OD) vs. superficial dot density relation. OD can also be a complicated function of wavelength. We measured half-tone microdot screens' and continuous materials' transmissions. Our set-up replicated the f/ 64 optical configuration of the Gemini Planet Imager's Apodized Pupil Lyot Coronagraph pupil plane, where we plan to place our pupil plane masks. Our half-tone samples were fabricated with 2, 5, and 10 micron dot sizes, our continuous greyscale was High Energy Electron Beam Sensitive (HEBS) glass (Canyon Materials Inc.). We present optical density (OD) vs. wavelength curves for our half-tone and continuous greyscale samples 1.1 - 2.5 μm wavelength range. Direct measurements of the beam intensity in the far field using a Fourier Transform Infrared Spectrograph on Beamline U4IR at Brookhaven National Laboratory's National Synchrotron Light Source (NSLS) provided transmission spectra of test patches and apodizers. We report the on-axis IR transmission spectra through screens composed of metallic dots that are comparable in size with the wavelength of the light used, over a range of optical densities. We also measured departures from simple theory describing the array of satellite spots created by thin periodic grids in the pupil of the system. Such spots are used for photometry and astrometry in coronagraphic situations. Our results pertain to both ground and space based coronagraphs that use spatially variable attenuation, typically in focal plane or pupil plane masks.
The optical design of MARVELS spectrograph
This paper describes an optical spectrograph design for the Multi-object APO Radial-Velocity Exoplanet Large-area Survey (MARVELS) instrument. This MARVELS instrument is currently installed at the Sloan 2.5m telescope, and is capable of simultaneously monitoring 60 stars at high radial velocity precision for a planet survey. The MARVELS spectrograph consists of an entrance slit (multi-slits), collimator optics, a Volume Phase Holographic (VPH) grating, camera optics and a 4kx4k CCD camera, which with a 160mm diameter collimated beam provides a spectral resolution of R =10000. This spectrograph is transmissive and optimized for delivering high throughput and high image quality over the entire operation bandwidth 500-570nm and the whole 160mmx30mm square shape FOV. The collimator and camera optics (280 mm largest diameter) are all made of standard optical grade glasses. The f/4 input beams from the MARVELS monolithic interferometer are converted to f/1.5 beams on the detector by this spectrograph, and form 120 stellar fringe spectra.
Optical design of a double pass cross-dispersed echelle spectrograph for extremely high precision extrasolar planet trackers
We describe the optical design and performance of a cross-dispersed echelle spectrograph designed to deliver high precision radial velocities. The spectrograph design enables two working modes, a Radial Velocity Mode (RVM) and a Direct Echelle Mode (DEM). The spectra resolving power of the RVM is R=18000 over 390nm-690nm when used with 1 arcsec slit, and delivering a R=27000 over 390nm-1000nm while using 0.6 arcsec slit for DEM. The focal ratio of this spectrograph is f/4 and the collimated beam diameter is 85mm. An R2 Echelle with 87 l/mm groove density and a 63 degree normal blaze angle will be used as the main disperse grating. A 45 degree PBM2Y prism operated in a double pass serves as a cross-disperser to separate the dispersion orders. Two objects spectra will be recorded on the top and bottom half of the one 4k by 4k CCD (15-micron pixel size) respectively in RVM, while one object spectra will be recorded on the same entire CCD. The total throughput of this spectrograph, in which consists of all spherical surface lenses is around 60%.
Modeling the image distortion of echelle spectrographs with T&P changes
Frank Grupp, ShaoMing Hu, Liang Wang
Even slight changes of temperature and pressure in high resolution ´Echelle spectrographs affect the spot image on the detector plane. At the same time astronomical applications require a stability of the measurement of up to 1/3000 of a pixel on the CCD (with a typical pixel size being 15μm). With this paper we present a study of the effects of thermal and pressure instabilities on ray tracing models of a typical ´Echelle spectrograph. We conclude the required minimum stabilty in these two parameters to reach the goal of precision spectroscopy.