We present a generalized non-negative factorization (NMF)-based data reduction pipeline for circumstellar disk and exoplanet detection. By using an adaptable pre-processing routine that applies algorithmic masks and corrections to improper data, we are able to easily offload the computationally-intensive NMF algorithm to a Graphics Processing Unit (GPU), significantly increasing computational efficiency. NMF has been shown to better preserve disk structural features compared to other post-processing approaches and has demonstrated improvements in the analysis of archival data. The adaptive pre-processing routine of this pipeline, which automatically aligns and applies image corrections to the raw data, is shown to significantly improve chromatic halo suppression. Utilizing HST-STIS and JWST-MIRI coronagraphic datasets, we demonstrate a factor of five increase in real-time computational efficiency by using GPUs to perform NMF compared to using CPUs. Additionally, we demonstrate the usefulness of higher numbers of NMF components with SNR and contrast improvements, which necessitates the use of a more computationally efficient approach for data reduction.
NASA’s next flagship mission, the Nancy Grace Roman Space Telescope, is a 2.4-meter observatory set to launch no later than May 2027. Roman features two instruments: the Wide Field Imager and the Coronagraph Instrument. The Roman Coronagraph is a Technology Demonstration that will push the current capabilities of direct imaging to smaller contrast ratios (∼10−9) and inner-working angles (3 λ/D). In order to achieve this high precision, Roman Coronagraph data must be calibrated to remove as many potential sources of error as possible. Here we present a detailed overview of the current plans for the Nancy Grace Roman Space Telescope Coronagraph Instrument Observation Calibration Plan, including identifying potential sources of error and how they will be mitigated via on-sky calibrations.
The Roman coronagraph instrument will demonstrate high-contrast imaging technology, enabling the imaging of faint debris disks, the discovery of inner dust belts, and planets. Polarization studies of debris disks provide additional information on dust grains’ size, distribution, and shape. The Roman coronagraph uses a polarization module comprising two Wollaston prism assemblies to produce four orthogonally polarized images (I0, I90, I45, and I135), each measuring 3.2 arcsecs in diameter and separated by 7.5 arcsecs in the sky. The expected RMS error in the linear polarization fraction measurement is 1.66% per resolution element of 3 by 3 pixels. We present a mathematical model to simulate the polarized intensity images through the Roman CGI, including the instrumental polarization and other uncertainties. We use disk modeling software, MCFOST, to model q, u, and polarization intensity of the debris disk, Epsilon-Eridani. The polarization intensities are convolved with the coronagraph throughput incorporating the PSF morphology. We include model uncertainties, detector noise, speckle noise, and jitter. The final polarization fraction of 0.4±0.0251 is obtained after post-processing and speckle noise removal.
The Nancy Grace Roman Space Telescope, planned to launch in the mid-2020s, will be the first space-based observatory to demonstrate active wavefront correction at high contrast with its Coronagraph Instrument. As a technology demonstrator, the instrument’s main purpose is to mature the various technologies needed by future flagship mission concepts that aim to image and characterize Earth-like exoplanets. These technologies include two high-actuator-count deformable mirrors (DMs), photon-counting detectors, two complementary wavefront sensing and control loops, and two different coronagraph types. Here we describe the complete set of flight mask designs for the Roman Coronagraph. Multiple mask configurations are required to overcome the challenging pupil obscurations and enable the desired types of imaging, spectroscopy, and polarimetry. In designing each mask configuration, we considered many performance metrics, including spectral bandwidth, field of view, contrast, core throughput, encircled energy, deformable mirror surface height, and low-order aberration sensitivity
KEYWORDS: Planets, Stars, Exoplanets, Imaging systems, Signal to noise ratio, Observatories, Telescopes, Target detection, Space telescopes, Monte Carlo methods
The addition of an external starshade to the Nancy Grace Roman Space Telescope will enable the direct imaging of Earth-radius planets orbiting at ∼1 AU. Classification of any detected planets as Earth-like requires both spectroscopy to characterize their atmospheres and multi-epoch imaging to trace their orbits. We consider here the ability of the Starshade Rendezvous Probe to constrain the orbits of directly imaged Earth-like planets. The target list for this proposed mission consists of the 16 nearby stars best suited for direct imaging, around which ∼10 to 15 planets are expected to be discovered. Of these planets, ∼1 to 2 will be Earth-like in mass and temperature. The field of regard for the starshade mission is constrained by solar exclusion angles, resulting in four observing windows during a two-year mission. We find that for Earth-like planets that are detected at least three times during the four viewing opportunities, their semi-major axes are measured with a median precision of 7 mas, or a median fractional precision of 3%. Habitable-zone planets can be correctly identified as such 96.7% of the time, with a false positive rate of 2.8%. If a more conservative criteria are used for habitable-zone classification (95% probability), the false positive rate drops close to zero, but with only 81% of the truly Earth-like planets correctly classified as residing in the habitable zone.
Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope (Roman) would provide the first opportunity to directly image the habitable zones (HZs) of nearby sunlike stars in the coming decade. A report on the science and feasibility of such a mission was recently submitted to NASA as a probe study concept. The driving objective of the concept is to determine whether Earth-like exoplanets exist in the HZs of the nearest sunlike stars and have biosignature gases in their atmospheres. With the sensitivity provided by this telescope, it is possible to measure the brightness of zodiacal dust disks around the nearest sunlike stars and establish how their population compares with our own. In addition, known gas-giant exoplanets can be targeted to measure their atmospheric metallicity and thereby determine if the correlation with planet mass follows the trend observed in the Solar System and hinted at by exoplanet transit spectroscopy data. We provide the details of the calculations used to estimate the sensitivity of Roman with a starshade and describe the publicly available Python-based source code used to make these calculations. Given the fixed capability of Roman and the constrained observing windows inherent for the starshade, we calculate the sensitivity of the combined observatory to detect these three types of targets, and we present an overall observing strategy that enables us to achieve these objectives.
The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will be capable of characterizing exoplanets in reflected light and will demonstrate space technologies essential for future missions to take spectra of Earthlike exoplanets. As the mission and instrument move into the final stages of design, simulation tools spanning from depth of search calculators to detailed diffraction models have been created by a variety of teams. We summarize these efforts, with a particular focus on publicly available datasets and software tools. These include speckle and point-spread-function models, signal-to-noise calculators, and science product simulations (e.g. predicted observations of debris disks and exoplanet spectra). This review is intended to serve as a reference to facilitate engagement with the technical and science capabilities of the CGI instrument.
The Coronagraph Instrument (CGI) on the Nancy Grace Roman Space Telescope will demonstrate the highcontrast technology necessary for visible-light exoplanet imaging and spectroscopy from space via direct imaging of Jupiter-size planets and debris disks. This in-space experience is a critical step toward future, larger missions targeted at direct imaging of Earth-like planets in the habitable zones of nearby stars. This paper presents an overview of the current instrument design and requirements, highlighting the critical hardware, algorithms, and operations being demonstrated. We also describe several exoplanet and circumstellar disk science cases enabled by these capabilities. A competitively selected Community Participation Program team will be an integral part of the technology demonstration and could perform additional CGI observations beyond the initial tech demo if the instrument performance warrants it.
The WFIRST Coronagraph Instrument (CGI) will image the environment close to stars at orders of magnitude higher sensitivity than current observatories. In addition to directly imaging giant exoplanets, WFIRST CGI has unprecedented sensitivity to scattered light from circumstellar dust. Most modeling has been confined to the dark-hole regime of the coronagraph (approximately 0.15 arcsec to 1 arcsec). This work uses publicly available field-dependent point spread functions to model an exozodiacal disk within the 0.15 arcsec inner working angle. For this simple Solar System-like test case, we find an approximately 25% increase in the transmitted exozodiacal flux due to light inside the inner working angle. We also describe plans to accelerate and extend this modeling to a wider range of geometries, and to quantify the impact on post-processing and source detection.
The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) is a high-contrast imager and integral field spectrograph that will enable the study of exoplanets and circumstellar disks at visible wavelengths. Future flagship mission concepts aim to image Earth analogues with visible light flux ratios greater than 10^10, and CGI is a critical intermediate step toward that goal. CGI will have ~3 months of observing time during the first 18 months of the mission (its "tech demo phase") to demonstrate its technology objectives and to determine whether its as-built performance justifies additional science observing time during the remainder of the mission. We present the CGI portion of the preliminary WFIRST Design Reference Mission (DRM). We describe the suite of anticipated observing and calibration tasks, the preliminary target list, and a schedule with realistic observing constraints and exposure times. We expect that during the tech demo phase CGI will image multiple planets and circumstellar disks in reflected light and take a spectrum of a mature Jupiter analog in reflected light. Furthermore, CGI is expected to be more sensitive than any previous instrument to extrasolar zodiacal dust and has the potential to study very young (proto)planetary systems.
KEYWORDS: Point spread functions, Stars, Coronagraphy, Speckle, Sensors, Telescopes, Signal to noise ratio, Space operations, Hubble Space Telescope, Charge-coupled devices
The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) contains the only currently operating coronagraph in space that is not trained on the Sun. In an era of extreme-adaptive-optics-fed coronagraphs, and with the possibility of future space-based coronagraphs, we re-evaluate the contrast performance of the STIS CCD camera. The 50CORON aperture consists of a series of occulting wedges and bars, including the recently commissioned BAR5 occulter. We discuss the latest procedures in obtaining high-contrast imaging of circumstellar disks and faint point sources with STIS. For the first time, we develop a noise model for the coronagraph, including systematic noise due to speckles, which can be used to predict the performance of future coronagraphic observations. Further, we present results from a recent calibration program that demonstrates better than 10 − 6 point-source contrast at 0.6″, ranging to 3 × 10 − 5 point-source contrast at 0.25″. These results are obtained by a combination of subpixel grid dithers, multiple spacecraft orientations, and postprocessing techniques. Some of these same techniques will be employed by future space-based coronagraphic missions. We discuss the unique aspects of STIS coronagraphy relative to ground-based adaptive-optics-fed coronagraphs.
The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) will be the first high-performance stellar coronagraph using active wavefront control for deep starlight suppression in space, providing unprecedented levels of contrast and spatial resolution for astronomical observations in the optical. One science case enabled by the CGI will be taking visible images and (R~50) spectra of faint interplanetary dust structures present in the habitable zone of nearby sunlike stars (~10 pc) and within the snow-line of more distant ones (~20 pc), down to dust brightness levels commensurate with that of the solar system zodiacal cloud. Reaching contrast levels below 10-7 at sub-arcsecond angular scales for the first time, CGI will cross an important threshold in debris disks physics, accessing disks with low enough optical depths that their structure is dominated by transport mechanisms rather than collisions. Hence, CGI will help us understand how exozodiacal dust grains are produced and transported in low-density disks around mature stars. Additionally, CGI will be able to measure the brightness level and constrain the degree of asymmetry of exozodiacal clouds around individual nearby sunlike stars in the optical, at the ~3x solar zodiacal emission level. This information will be extremely valuable for optimizing the observational strategy of possible future exo-Earth direct imaging missions, especially those planning to operate at optical wavelengths as well, such as the Habitable Exoplanet Observatory (HabEx) and the Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR).
The WFIRST mission was originally ended as a wide-field survey facility. With the change to a 2.4-m telescope, the mission is capable of carrying an effective coronagraph for exoplanet imaging. The baseline architecture allows use of a hybrid lyot or shaped pupil coronagraph, feeding a imager and integral field spectrograph. This will allow imaging and photometry of mature nearby planets and zodiacal disks in reflected light, as well as spectroscopy of the brightest targets. I will discuss the scientific motivations of the mission and show simulated science capabilities, and discuss the process towards definition of a science mission.
In the past 20 years, the Hubble Space Telescope (HST) STIS coronagraphic instrument has observed more than 100 stars, obtaining more than 4,000 readouts since its installment on HST in 1997 and the numbers are still increasing. We reduce the whole STIS coronagraphic archive at the most commonly observed positions (Wedge A0.6 and A1.0) with new post-processing methods, and present our results here. We are able to recover all of the 32 previously reported circumstellar disks, and obtain better contrast close to the star. For some of the disks, our results are limited by the over subtraction of the methods, and therefore the major regions of the disks can be recovered except the faintest regions. We also explain our efforts in the calibration of its new BAR5 occulting position, enabling STIS to explore inner regions as close as 0.2 00 .
KEYWORDS: Coronagraphy, James Webb Space Telescope, Point spread functions, Space telescopes, Telescopes, Infrared telescopes, Stars, Sensors, Space operations, Astronomical telescopes
The coronagraphic instrument (CGI) currently proposed for the Wide-Field Infrared Survey Telescope–Astrophysics Focused Telescope Assets (WFIRST-AFTA) mission will be the first example of a space-based coronagraph optimized for extremely high contrasts that are required for the direct imaging of exoplanets reflecting the light of their host star. While the design of this instrument is still in progress, this early stage of development is a particularly beneficial time to consider the operation of such an instrument. We review current or planned operations on the Hubble Space Telescope and the James Webb Space Telescope with a focus on which operational aspects will have relevance to the planned WFIRST-AFTA CGI. We identify five key aspects of operations that will require attention: (1) detector health and evolution, (2) wavefront control, (3) observing strategies/postprocessing, (4) astrometric precision/target acquisition, and (5) polarimetry. We make suggestions on a path forward for each of these items.
The Far Ultraviolet (FUV) detector on the Cosmic Origins Spectrograph (COS) of the Hubble Space Telescope (HST) is subject to a variety of distortions due to its analog nature. Thermal variations of the detector and electronics stretch and shift the active area. Geometric distortions on a range of spatial scales warp the two-dimensional spectral image. Changes due to detector walk – the dependence of detected position on pulse height – add distortions that change as a function of time. The calcos calibration pipeline includes corrections for each of these effects in the calibrated spectra, but these are imperfect, and they do not help with the target acquisition process, which uses raw detector coordinates. We discuss these distortions and their effect on the data, our attempts to mitigate them, the current pipeline corrections and their success at removing the effects, and possible modifications to improve the data quality in the future.
KEYWORDS: Point spread functions, Stars, Coronagraphy, Databases, Planets, Space telescopes, Telescopes, Image processing, Signal to noise ratio, Target detection
We are currently conducting a comprehensive and consistent re-processing of archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction methods, entitled the Archival Legacy Investigations of Circumstellar Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400 targets has already produced numerous new detections of previously unidentified point sources and circumstellar structures. We present five newly spatially resolved debris disks revealed in scattered light by our analysis of the archival data. These images provide new views of material around young solar-type stars at ages corresponding to the period of terrestrial planet formation in our solar system. We have also detected several new candidate substellar companions, for which there are ongoing followup campaigns (HST/WFC3 and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are directly applicable to future missions (JWST, AFTA coronagraph) we emphasize the importance of devising optimal PSF subtraction methods for upcoming coronagraphic imaging missions. We describe efforts in defining direct imaging high-level science products (HLSP) standards that can be applicable to other coronagraphic campaigns, including ground-based (e.g., Gemini Planet Imager), and future space instruments (e.g., JWST). ALICE will deliver a first release of HLSPs to the community through the MAST archive at STScI in 2014.
David Sahnow, Alessandra Aloisi, K. Azalee Bostroem, John Debes, Justin Ely, Philip Hodge, Gerard Kriss, Derck Massa, Cristina Oliveira, Rachel Osten, Steven Osterman, Steven Penton, Charles Proffitt, Julia Roman-Duval, Paule Sonnentrucker
The Far Ultraviolet (FUV) detector of the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST)
uses a large-format, two-segment microchannel plate detector with a Cross Delay-Line anode. Since the installation of
COS into HST in 2009, the detector’s properties have continually evolved, and changes to both sensitivity and
microchannel plate gain have been observed. In order to maximize the lifetime of the detector, we have been monitoring
its local properties as a function of time, cumulative exposure, and other factors, and we have constructed models to
predict its future evolution. These models will allow us to actively manage the microchannel plate high voltage levels
and the location of the spectra on the detector in order to extend its life without limiting its scientific use. We are also
tracking the global sensitivity of the detector, which has been decreasing since installation; the rate of degradation has
been found to vary with time, and appears to be correlated with solar activity.
David Sahnow, Alessandra Aloisi, K. Azalee Bostroem, John Debes, Julia Duval, Justin Ely, Philip Hodge, Gerard Kriss, Kevin Lindsay, Derck Massa, Cristina Oliveira, Rachel Osten, Steven Osterman, Steven Penton, Charles Proffitt, Paule Sonnentrucker, Brian York
The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope in May 2009, and has been
collecting ultraviolet spectra since then. The Far Ultraviolet channel of COS uses an efficient optical design and a two-segment,
large-format Cross Delay Line microchannel plate detector to obtain spectra at medium and low resolution in
the far ultraviolet. While the overall instrument performance has been excellent, several long-term trends in performance
have been noted and are being addressed. These include a slow decrease in overall sensitivity, which is independent of
the illumination and may be due to a degradation of the photocathode with time.
In addition, the detector microchannel plates are showing severe gain sag in the regions where the most photons have
fallen. As a result, we are in the process of moving the spectra to a new, nearly pristine, location on the detector. This
will be the first of several additional lifetime positions which will allow us to collect high-quality spectra for many years
to come. We will discuss the factors that led to our decision on where to move next and our progress in moving there,
including details of the enabling and calibration activities which are being performed at the new location, and the
anticipated performance. We will also address strategies that will be implemented in order to prolong the life at this and
subsequent positions.
We report progress on development of a new generation of binary band-limited coronagraphic image masks at Penn State for extremely high contrast imaging of extrasolar planets with future visible Terrestrial Planet Finder (TPF). The masks are being precisely fabricated with a state-of-the-art E-beam lithographer using ~20 nm precision and are capable of achieving contrasts of 10-9 with high throughput (> 40%) and close inner working distance (3 λ/D). A prototype with 250 nm precision has allowed us to reach ~10-6 contrast at 8 λ/D and 10-5 at 3 λ/D with ~27% throughput (Debes et al. 2004).
We present the first lab experiments using a notch filter mask, a coronagraphic mask that dims the light from an on-axis source while passing off-axis light unscathed. The notch filter mask is essentially an optimized Lyot coronagraph that diffracts all of the light from the central object into a small ring that can be blocked by a Lyot stop. Notch filter masks provide a high throughput, very high contrast alternative to traditional Lyot coronagraphs. These masks, like all methods for achieving high contrast, require a high amount of accuracy in design to be successful. Nanofabrication techniques can meet these design challenges; with the first notch filter mask prototype fabricated with .25 μm precision using an e-beam lithography machine. When placed in a test bed, initial results show that 10-5 contrast is achieved at 3λ/Δ and 10-6 at ~8λ/Δ with a throughput of 27%. The coronagraph rejects light from the point source's peak by at least 4 orders of magnitude despite leakage of light through the mask. We speculate on the "as-is" performance of such a mask
in the Hubble Space Telescope.
A versatile near IR instrument called Penn State near IR Imager and Spectrograph (PIRIS) with a 256 x 256 PICNIC IR array has been developed at Penn State and saw its first light at the Mt. Wilson 100 inch in October 2001. The optical design consists of five optical subsystems including (1) the slit aperture wheel, (2) an achromat collimator optic, (3) a grism/filter and pupil assembly, (4) a pupil imaging optic, and (5) achromat camera optics. This instrument has imaging, spectroscopy and coronagraph modes. It is being updated to have an integral field 3-D imaging spectroscopy mode and a very high IR spectroscopy mode (R ~ 150,000) with an anamorphic silicon immersion grating in 2003. The instrument is designed to take full advantage of high Strehl ratio images delivered by high order adaptive optics systems. Its imaging mode has f/37 and f/51 optics to allow diffraction-limited imaging in H and K bands, respectively. Its spectroscopy mode has R = 20, 180, 400, 2000, and 5000. The lowest resolution is obtained with a non-deviation prism. The medium resolution spectroscopy mode is conducted with three commercial fused-silica grisms. They can be either used in long slit spectroscopy mode with a blocking filter or used as a cross-disperser for a high resolution silicon grism. High resolution spectroscopy is done with silicon grisms and cross-disperser grisms, which are designed to work on high orders (~ 80) to completely cover H and K bands for R = 5000 separately, or simultaneously cover H and K bands for R = 2000. Coronagraphy is done by inserting an apodizing mask, held in the slit aperture wheel, in the focal plane and a Lyot stop (pupil mask) at a reimaged pupil inside the dewar. Image contrast can be enhanced by using different combinations of the apodizing mask and pupil mask. Several of Gaussian pupil masks have also been installed in the pupil wheel for high contrast imaging. We have successfully detected two substellar companions during our first light at Mt. Wilson 100 inch telescope. We were also able to evaluate our cononagraphy and gaussion pupil mask modes, which demonstrate 10-3 - 10-4 contrast 1 arcsec region around a bright point source. A hybrid coronagraph mode, a combination of an apodizing focal plane mask with a Gaussian shaped pupil mask, has been tested and produces 10-5 - 10-6 deep contrast as close as 4 λ/D at 2.2 μm in the lab. Low resolution spectroscopy modes including a vision prism (R = 20) and three fused silicon grisms (R = 200 - 400) have been tested in the lab. The spectroscopy results are reported here.
At Penn State, two new instrument component technologies, namely silicon gratings and gaussian-shaped pupil masks, have been developed and are ready for producing high quality components for all three NGST IR instruments. Fabrication of silicon grisms with sizes up to 2 inches in dimension has become a routine process at Penn State thanks to newly developed techniques in chemical etching, lithography, and post-processing. The newly etched silicon grisms have a typical rms surface roughness of ~ 9 nm with the lowest of 0.9 nm, significantly lower than our previous ones (~ 20-30 nm) and have ~ 0.035 wave wavefront distortion at 0.6328 μm, indicating diffraction-limited performance in the entire infrared wavelengths (1.2 -10 μm) where silicon has excellent transmission. These processes have also significantly eliminated visible defects due to grating mask break during chemical etching. For the best grisms, we have less than 1 defect per cm2. The measured total integrated scatter is less than 1% at 0.6238 mm, indicating similar or lower scatter in the IR when grisms are operated in transmission. Silicon grisms and silicon immersion gratings will both boost spectral resolving power by more than 3 times for NGST near-IR MOS and mid-IR camera and spectrograph without pushing current instrument design. The higher dispersed spectra can be selected either by a filter or a low resolution grism cross-disperser. Our current grating techniques allow us to make gratings with a groove period from a few microns to more than 100 microns. For the first order grism, the theoretical grating efficiency is beyond 80% with a single layer of AR coating. The immersion gratings will have similar grating efficiency. Based on our previous measurements of a silicon echelle grism, this kind of grism can provide ~ 60% efficiency when they are operated in high orders.
We have also developed Gaussian-shaped pupil masks for high contrast imaging with the NGST IR cameras. Depending on its final mirror configuration, this kind of mask can offer 10-6 contrast imaging as close as 5 lambda/D to a bright point source. The advantage of using this mask instead of a conventional graded Lyot coronagraph is that it is much easier to implement by simply inserting it at a pupil location to reach deep null. Therefore, the observing efficiency can be significantly improved. A prototype of this kind of mask has been tested at the Mt. Wilson 100inch telescope with adaptive optics and demonstrates 10-3-10-4 contrast at ~ 5 λ/D at the initial observations. The contrast level is comparable to an IR coronagraph in the same IR instrument, but is about one order of magnitude worse than the scattered light levels caused by the mirror surface. We have also studied other mask coronagraph designs for high contrast imaging. The hybrid and band-limited designs show great promise for further improving image contrast. The NGST IR cameras with new coronagraph designs will allow high contrast imaging for extra-solar planets and substellar companions around nearby stars.
Gaussian aperture pupil masks can in theory achieve the contrast requisite for directly imaging an extrasolar planet. We outline the process of fabricating and testing a GAPM for use on the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100" telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph without blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF to within an order of magnitude and with new designs achieve ~5×10-5 contrast at 10λ/D. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribut ehe most degradation to contrast. Finally we compare the performance of GAPMs and Lyot coronagrphs of similar throughput.
A combination of Spergel’s innovative gaussian-shaped pupil masks with future space-based and ground-based adaptive optics telescopes will offer great sensitivity for direct imaging of faint companions including brown dwarfs and extra-solar planets around nearby stars. Here we propose a quick way to fully achieve its potential for deep contrast imaging surveys with a great speed in a conventionally designed telescope. In our approach, two Gaussian pupil masks set on each side of the secondary obscuration, slightly penetrating the telescope spider structures, are placed in a cryogenic pupil plane in an infrared (IR) camera to allow the collimated telescope beams to pass through. This simple design will enable ~10-6 deep contrast imaging while enjoying diffraction-limited imaging from the full telescope aperture for discovering faint companions closest to the primary. The survey speed with this design will be at least 3-4 times faster than a conventional coronagraph due to its simple alignment. This contrast should allow an image survey for Jupiter-like planets to ~ 20 pc in the thermal IR with next generation large ground-based and space based telescopes. A combination of this shaped pupil mask with an apodizing focal plane mask will enable deeper contrast than the pupil mask alone. However, it takes a much longer time to align the system, so this mode will be used for characterization of faint companion systems from the candidates identified from the survey.
A prototype gaussian pupil mask in the Penn State near IR Imager and Spectrograph (PIRIS) has been tested at the Mt. Wilson 100 inch telescope with high order natural guide star adaptive optics (AO) and has demonstrated its tremendous potential. The contrast is about 10-3-10-4 beyond 7 λ/Δ. The contrast is about 5 times better than the direct AO image, and comparable to an IR coronagraph in the same instrument. Recent lab experiments show that 3x10-6 at ~ 4 λ/Δ can be reached with a combination of a Gaussian pupil mask with an apodizing focal plane mask.
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