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Starshade Imaging Simulation Toolkit for Exoplanet Reconnaissance (SISTER) is a versatile tool designed to provide accurate models of the images of exoplanet systems when observed with a starshade positioned to block the light from the host star. SISTER allows one to control a set of observational parameters including: (1) the starshade design, position, orientation, and glint properties; (2) the telescope and optical system pupil, aberrations, bandpass, and throughput including a detector model; (3) the exoplanetary system, including stellar distance and spectral type, parallax and proper motion, planet size, reflection properties, orbital parameters, and exozodiacal dust; and (4) background objects. Additionally, there is a substantial library of built-in plotting software added, but the simulations may be stored on disk and plotted with any other software. We describe SISTER’s algorithms, its operational modules, and how it can be used to generate starshade optical simulations with a high degree of fidelity. We include some imaging examples.

Starshade in formation flight with a space telescope is a rapidly maturing technology that would enable imaging and spectral characterization of small planets orbiting nearby stars in the not-too-distant future. While performance models of starshade-assisted exoplanet imaging have been developed and used to design future missions, their results have not been verified from the analyses of synthetic images. Following a rich history of using community data challenges to evaluate image-processing capabilities in astronomy and exoplanet fields, the Starshade Technology Development to TRL5 (S5), a focused technology development activity managed by the NASA Exoplanet Exploration Program, is organizing and implementing a starshade exoplanet data challenge. The purpose of the data challenge is to validate the flow down of requirements from science to key instrument performance parameters and to quantify the required accuracy of noisy background calibration with synthetic images. This data challenge distinguishes itself from past efforts in the exoplanet field in that (1) it focuses on the detection and spectral characterization of small planets in the habitable zones of nearby stars, and (2) it develops synthetic images that simultaneously include multiple background noise terms—some observations specific to starshade—including residual starlight, solar glint, exozodiacal light, detector noise, as well as variability resulting from starshade’s motion and telescope jitter. We provide an overview of the design and rationale of the data challenge. Working with data challenge participants, we expect to achieve improved understanding of the noise budget and background calibration in starshade-assisted exoplanet observations in the context of both starshade rendezvous with Roman and Habitable Exoplanet Observatory. This activity will thus help NASA prioritize further technology developments and prepare the science community for analyzing starshade exoplanet observations.

Starshades are a leading technology to enable the detection and spectroscopic characterization of Earth-like exoplanets. In this paper we report on optical experiments of sub-scale starshades that advance critical starlight suppression technologies in preparation for the next generation of space telescopes. These experiments were conducted at the Princeton starshade testbed, an 80 m long enclosure testing 1/1000th scale starshades at a flight-like Fresnel number. We demonstrate 1e-10 contrast at the starshade's geometric inner working angle across 10% of the visible spectrum, with an average contrast at the inner working angle of 2.0e-10 and contrast floor of 2e-11. In addition to these high contrast demonstrations, we validate diffraction models to better than 35% accuracy through tests of intentionally flawed starshades. Overall, this suite of experiments reveals a deviation from scalar diffraction theory due to light propagating through narrow gaps between the starshade petals. We provide a model that accurately captures this effect at contrast levels below 1e-10. The results of these experiments demonstrate that there are no optical impediments to building a starshade that provides sufficient contrast to detect Earth-like exoplanets. This work also sets an upper limit on the effect of unknowns in the diffraction model used to predict starshade performance and set tolerances on the starshade manufacture., Comment: 67 pages; 25 figures; submitted to Journal of Astronomical Telescopes, Instruments, and Systems

High-contrast imaging enabled by a starshade in formation flight with a space telescope can provide a near-term pathway to search for and characterize temperate and small planets of nearby stars. NASA's Starshade Technology Development Activity to TRL5 (S5) is rapidly maturing the required technologies to the point at which starshades could be integrated into potential future missions. Here we reappraise the noise budget of starshade-enabled exoplanet imaging to incorporate the experimentally demonstrated optical performance of the starshade and its optical edge. Our analyses of stray light sources - including the leakage through micrometeoroid damage and the reflection of bright celestial bodies - indicate that sunlight scattered by the optical edge (i.e., the solar glint) is by far the dominant stray light. With telescope and observation parameters that approximately correspond to Starshade Rendezvous with Roman and HabEx, we find that the dominating noise source would be exozodiacal light for characterizing a temperate and Earth-sized planet around Sun-like and earlier stars and the solar glint for later-type stars. Further reducing the brightness of solar glint by a factor of 10 with a coating would prevent it from becoming the dominant noise for both Roman and HabEx. With an instrument contrast of 1E-10, the residual starlight is not a dominant noise; and increasing the contrast level by a factor 10 would not lead to any appreciable change in the expected science performance. If unbiased calibration of the background to the photon-noise limit can be achieved, Starshade Rendezvous with Roman could provide nearly photon-limited spectroscopy of temperate and Earth-sized planets of F, G, and K stars, Accepted for publication in the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

Starshade concepts must be stowed within rocket fairings for launch and then deployed in space. The in-plane deployment accuracy must be on the order of hundreds of micrometers for sufficient starlight suppression to enable the detection and study of Earth-like exoplanets around nearby Sun-like stars. We describe tests conducted to demonstrate deployment repeatability of two key structural subsystems of the “furled” starshade architecture—the petal and the inner disk. Together, the petals and the inner disk create the in-plane shape of a starshade. Test articles to represent the petal and inner disk subsystems were constructed at relevant scales for a 26-m-diameter starshade. These test articles were subjected to stowage-and-deployment cycles and their shapes were measured. The measured performance—tens of parts per million of petal strain after deployment, and hundreds of micrometers of inner disk deployment accuracy—was found to be within required allocations.

Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope would provide the first opportunity to directly image the habitable zones 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 habitable zones 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 to 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. In this paper 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., Accepted for publication in the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

Starshades are a leading technology to detect and characterize Earth-like exoplanets. In this paper we report on optical experiments of sub-scale starshades that advance critical starlight suppression technologies in preparation for the next generation of space telescopes. These experiments were conducted at the Princeton starshade testbed, an 80 m long enclosure testing 1/1000th scale starshades at a flight-like Fresnel number. In this paper we summarize recent updates made to the starshade testbed and optical model. We present results from recent experiments testing two starshade masks with intentional perturbations built into their shape. One of the perturbed masks has three petals that are shifted radially outward by 7-11 microns and the other mask has two petals shifted radially outward plus two petal edge segments displaced from their nominal position. We show the model agrees with experiment to better than 25% accuracy. These results are placed into context with previous experiments on perturbed shapes and progress made towards satisfying a critical milestone in advancing starshade technology to TRL 5.

Stellar coronagraphs rely on deformable mirrors (DMs) to correct wavefront errors and create high contrast images. Imperfect control of the DM limits the achievable contrast and, therefore, the DM control electronics must provide fine surface height resolution and low noise. Here, we study the impact of quantization errors due to the DM electronics on the image contrast using experimental data from the High Contrast Imaging Testbed (HCIT) facility at NASA's Jet Propulsion Laboratory (JPL). We find that the simplest analytical model gives optimistic predictions compared to real cases, with contrast up to 3 times better, which leads to DM surface height resolution requirements that are incorrectly relaxed by 70%. We show that taking into account the DM actuator shape, or influence function, improves the analytical predictions. However, we also find that end-to-end numerical simulations of the wavefront sensing and control process provide the most accurate predictions and recommend such an approach for setting robust requirements on the DM control electronics. From our experimental and numerical results, we conclude that a surface height resolution of approximately 6pm is required for imaging temperate terrestrial exoplanets around Solar-type stars at wavelengths as small as 450nm with coronagraph instruments on future space telescopes. Finally, we list the recognizable characteristics of quantization errors that may help determine if they are a limiting factor.

A key challenge for starshades is formation flying. To successfully image exoplanets, the telescope boresight and starshade must be aligned to ∼1 m at separations of tens of thousands of kilometers. This challenge has two parts: first, the relative position of the starshade with respect to the telescope must be sensed; second, sensor measurements must be combined with a control law to keep the two spacecraft aligned in the presence of gravitational and other disturbances. In this work, we present an optical sensing approach using a pupil imaging camera in a 2.4-m telescope that can measure the relative spacecraft bearing to a few centimeters in 1 s, much faster than any relevant dynamical disturbances. A companion paper will describe how this sensor can be combined with a control law to keep the two spacecraft aligned with minimal interruptions to science observations.

Coronagraph instruments on future space telescopes will enable the direct detection and characterization of Earth-like exoplanets around Sun-like stars for the first time. The quest for the optimal optical coronagraph designs has made rapid progress in recent years thanks to the Segmented Coronagraph Design and Analysis (SCDA) initiative led by the Exoplanet Exploration Program at NASA's Jet Propulsion Laboratory. As a result, several types of high-performance designs have emerged that make use of dual deformable mirrors to (1) correct for optical aberrations and (2) suppress diffracted starlight from obstructions and discontinuities in the telescope pupil. However, the algorithms used to compute the optimal deformable mirror surface tend to be computationally intensive, prohibiting large scale design surveys. Here, we utilize the Fast Linearized Coronagraph Optimizer (FALCO), a tool that allows for rapid optimization of deformable mirror shapes, to explore trade-offs in coronagraph designs for obstructed and segmented space telescopes. We compare designs for representative shaped pupil Lyot and vortex coronagraphs, two of the most promising concepts for the LUVOIR space mission concept. We analyze the optical performance of each design, including their throughput and ability to passively suppress light from partially resolved stars in the presence of low-order aberrations. Our main result is that deformable mirror based apodization can sufficiently suppress diffraction from support struts and inter-segment gaps whose widths are on the order of $\sim$0.1% of the primary mirror diameter to detect Earth-sized planets within a few tens of milliarcseconds from the star., To appear in the Proceedings of the SPIE, vol. 10698

Starshades provide a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Two key aspects to advancing starshade technology are the demonstration of starlight suppression at science-enabling levels and validation of optical models at this high level of suppression. These technologies are addressed in current efforts underway at the Princeton Starshade Testbed. Recent experimental data suggest we are observing the effects of vector (non-scalar) diffraction, which are limiting the starshade's performance and preventing the scalar optical models from agreeing with experimental results at the deepest levels of suppression. This report outlines a model developed to simulate vector diffraction in the testbed using a full solution to Maxwell's equations propagating through narrow features of the starshade. We find that experimental results can be explained by vector diffraction as light traverses the thickness of the starshade mask and that our model is in rough agreement with observations. We provide simulation results of a number of starshade geometries as a first attempt to understand the relation of these effects to properties of the starshade masks. Finally, we outline a number of possible solutions aimed to minimize vector effects and to allow us to reach our milestone of 10-9 suppression.

A coronagraphic starlight suppression system situated on a future flagship space observatory offers a promising avenue to image Earth-like exoplanets and search for biomarkers in their atmospheric spectra. One NASA mission concept that could serve as the platform to realize this scientific breakthrough is the Large UV/Optical/IR Surveyor (LUVOIR). Such a mission would also address a broad range of topics in astrophysics with a multiwavelength suite of instruments. The apodized pupil Lyot coronagraph (APLC) is one of several coronagraph design families that the community is assessing as part of NASAs Exoplanet Exploration Program Segmented aperture coronagraph design and analysis (SCDA) team. The APLC is a Lyot-style coronagraph that suppresses starlight through a series of amplitude operations on the on-axis field. Given a suite of seven plausible segmented telescope apertures, we have developed an object-oriented software toolkit to automate the exploration of thousands of APLC design parameter combinations. This has enabled us to empirically establish relationships between planet throughput and telescope aperture geometry, inner working angle, bandwidth, and contrast level. In parallel with the parameter space exploration, we have investigated several strategies to improve the robustness of APLC designs to fabrication and alignment errors. We also investigate the combination of APLC with wavefront control or complex focal plane masks to improve inner working angle and throughput. Preliminary scientific yield evaluations based on design reference mission simulations indicate the APLC is a very competitive concept for surveying the local exoEarth population with a mission like LUVOIR., 17 pages, 16 figures, SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

The HabEx (Habitable Exoplanet Imaging Mission) study is developing concepts for a next generation space telescope operating from the ultraviolet to the infrared. HabEx is making exoplanet science the primary mission objective and adding two secondary payload instruments for general astrophysics, including ultraviolet spectroscopy. For exoplanet work, two approaches are being developed. The first is a coronagraph with two separate channels to cover a broad spectral range from 450 nm to 1000 nm in two observations. The second is a starshade to cover the band 300 nm to 1000 nm in a single observation. These instruments are complementary; the coronagraph can make rapid survey observations while the starshade can reach closer in to the star and once on target, enables more efficient spectroscopic observations. This paper describes some of the key design considerations necessary to enable coronagraph and starshade observations.

Future searches for biomarkers on habitable exoplanets will rely on telescope instruments that achieve extremely high contrast at small planet-to-star angular separations. Coronagraphy is a promising starlight suppression technique, providing excellent contrast and throughput for off-axis sources on clear apertures. However, the complexity of space- and ground-based telescope apertures goes on increasing over time, owing to the combination of primary mirror segmentation, secondary mirror, and support structures. These discontinuities in the telescope aperture limit the coronagraph performance. In this paper, we present ACAD-OSM, a novel active method to correct for the diffractive effects of aperture discontinuities in the final image plane of a coronagraph. Active methods use one or several deformable mirrors that are controlled with an interaction matrix to correct for the aberrations in the pupil. However, they are often limited by the amount of aberrations introduced by aperture discontinuities. This algorithm relies on the recalibration of the interaction matrix during the correction process to overcome this limitation. We first describe the ACAD-OSM technique and compare it to the previous active methods for the correction of aperture discontinuities. We then show its performance in terms of contrast and off-axis throughput for static aperture discontinuities (segmentation, struts) and for some aberrations evolving over the life of the instrument (residual phase aberrations, artifacts in the aperture, misalignments in the coronagraph design). This technique can now obtain the earth-like planet detection threshold of 10^(-10) contrast on any given aperture over at least a 10% spectral bandwidth, with several coronagraph designs., Comment: 14 pages, 21 figures, accepted for publication in The Astronomical Journal

The Space Interferometry Mission is an optical stellar interferometer with a 10 meter baseline capable of micro-arcsecond accuracy astrometry.

In the era of large telescopes and RV/Transit planetary missions, nulling interferometry remains a competitive technique for the characterization of Earths and Super-earths around Sun analogs in the mid-IR (Leger 2015, ApJ 808, 194). This is a spectral range where a number of bio-signatures can be accessed from space. One challenge of nulling is to benefit from well-established and qualified infrared fibers and integrated optics capable of mitigating the instrumental constraints on the beam combination and wavefront filtering to reach high extinction ratios. Such photonics devices have reached high maturity in the near-IR range as in the case of the integrated optics (IO) beam combiner of GRAVITY at the VLTI, leading to unprecedented interferometric accuracy. Driven by the need of next-generation interferometers, we expand the photonic approach towards longer wavelengths and develop IO combiners based on the ultrafast laser writing technique. We developed single-mode, low-loss evanescent couplers in gallium lanthanum sulfide with a 50/50 splitting behavior around 3.4 µm and characterized the intrinsic chromaticity by FTS. High monochromatic and broadband contrasts are measured with unpolarized light at 3.39µm (>98%), over the L band (>95%), and over the M Band (4.5-4.8µm) (>95%). Our analysis of the interferometric visibilities and phase shows a small differential birefringence in the component and negligible differential dispersion. This results points out the promising properties of mid-infrared laser writing integrated optics devices to serve as high quality beam combiners. The extension to a four-aperture architecture appears plausible, with care to be taken about the impact of the design on the total throughput.

The Theia mission, as a natural successor to Gaia, will be the first extremely-high-precision astrometric surveyor that may emerge from the last ESA M5 call in October 2016. A major objective of Theia in the context of this conference is the detection by astrometry of Earths and Super-Earths exoplanets in the habitable zone of nearby A to M stars. This can be done by astrometry from space if a motion of

The SCExAO system is a flexible high contrast imaging platform for exoplanet imaging on the 8-m Subaru Telescope. SCExAO's wavefront control architecture relies on both visible and infrared wavefront sensors to measure, correct and calibrate wavefront errors. The wavefront control loop, optimized for high contrast imaging, includes predictive control, sensor fusion and focal plane speckle control to address the performance limits of current extreme-AO systems: non-common path errors, time-lag and chromaticity. The control software is also designed to enable rapid prototyping of new wavefront algorithm, as one goal of the SCExAO project is to explore and validate new high contrast imaging approaches to guide the design of future ELT high contrast imaging systems. We describe the SCExAO wavefront control architecture and its software implementation. Recent on-sky results are presented, and future steps are describted. Current and future high contrast imaging performance are provided. We discuss findings (lessons learned) in the context of future exoplanet imaging instrument developments.

Based on the experience from Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) for WFIRST, we have moved to the flight instrument design phase. The flight instrument is similar to PISCES, but there are important changes to its design as our requirements have evolved. Beginning with the science and system requirements, we discuss a number of critical trade-offs. Most significantly there are trades in the type of IFS, lenslet array shape and layout, detector sampling, and accommodating the larger Field Of View (FOV) and wider wavelength band for a potential Starshade. Finally, the traditional geometric optical design is also investigated and traded. We compare a reflective versus refractive design, and the telecentricity of the relay. The relay before the lenslet array controls the chief angle distribution on the lenslet array. Our previous paper1 has addressed how the relay design combined with lenslet array/pinhole mask can further suppress the residual star light and increase the contrast. Highlighting all of these design trades, we present the phase A IFS optical design for the WFIRST coronagraph instrument.

Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Two key aspects to advancing starshade technology are the demonstration of starlight suppression to the level required for flight and validation of optical models at this high level of suppression. These technologies are addressed in current efforts underway at the Princeton Starshade Testbed. We report on results from modeling the performance of the Princeton Starshade Testbed to help achieve the milestone 10−9 suppression. We use our optical model to examine the effects that errors in the occulting mask shape and external environmental factors have on the limiting suppression. We look at deviations from the ideal occulter shape such as over-etching during the lithography process, edge roughness of the mask, and random defects introduced during manufacturing. We also look at the effects of dust and wavefront errors in the open-to-atmosphere testbed. These results are used to set fabrication requirements on the starshade and constraints on the testbed environment. We use detailed measurements of the manufactured occulting mask to converge towards agreement between our modeled performance predictions and the suppression measured in the testbed, thereby building confidence in the validity of the optical models. We conclude with a discussion of the advantages and practicalities of scaling to a larger testbed to further advance the optical aspect of starshade technology.

Starshades are external occulters which would be used in conjunction with a space telescope. The starshade has a particular apodizing profile that effects strong suppression of starlight within the starshade's shadow. Since starshades that would be used in space are large, typically 30 m diameter or more, performance is difficult to test on the ground at realistic scales. This paper examines the practical limits for testing starshades at smaller scales in the atmosphere and goes on to describe concepts for testing starshades using ground based telescopes and using starshades for astronomical observations.

Directly imaging and characterizing Earth-like exoplanets is a tremendously difficult instrumental challenge. Present coronagraphic systems have yet to achieve the required 10 − 10 broadband contrast in a laboratory environment, but promising progress toward this goal continues. An approach to starlight suppression is the use of a single-mode fiber (SMF) behind a coronagraph. By using deformable mirrors to create a mismatch between incoming starlight and the fiber mode, SMF can be turned into an integral part of the starlight suppression system. We present simulation results of a system with five SMFs coupled to shaped pupil and vortex coronagraphs. We investigate the properties of the system, including its spectral bandwidth, throughput, and sensitivity to low-order aberrations. We also compare the performance of the SMF configuration with conventional imaging and multiobject modes, finding improved spectral bandwidth, raw contrast, background-limited signal-to-noise ratio, and demonstrate a wavefront control algorithm, which is robust to tip/tilt errors.

Current state-of-the-art high contrast imaging instruments take advantage of a number of elegant coronagraph designs to suppress starlight and image nearby faint objects, such as exoplanets and circumstellar disks. The ideal performance and complexity of the optical systems depends strongly on the shape of the telescope aperture. Unfortunately, large primary mirrors tend to be segmented and have various obstructions, which limit the performance of most conventional coronagraph designs. We present a new family of vortex coronagraphs with numerically-optimized gray-scale apodizers that provide the sensitivity needed to directly image faint exoplanets with large, segmented aperture telescopes, including the Thirty Meter Telescope (TMT) as well as potential next-generation space telescopes., Comment: To appear in SPIE proceedings vol. 9912

We are undertaking an astrometric search for gas giant planets and brown dwarfs orbiting nearby low mass dwarf stars with the 2.5-m du Pont telescope at the Las Campanas Observatory in Chile. We have built two specialized astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S and CAPSCam-N), using two Teledyne Hawaii-2RG HyViSI arrays, with the cameras' design having been optimized for high accuracy astrometry of M dwarf stars. We describe two independent CAPSCam data reduction approaches and present a detailed analysis of the observations to date of one of our target stars, NLTT 48256. Observations of NLTT 48256 taken since July 2007 with CAPSCam-S imply that astrometric accuracies of around 0.3 milliarcsec per hour are achievable, sufficient to detect a Jupiter-mass companion orbiting 1 AU from a late M dwarf 10 pc away with a signal-to-noise ratio of about 4. We plan to follow about 100 nearby (primarily within about 10 pc) low mass stars, principally late M, L, and T dwarfs, for 10 years or more, in order to detect very low mass companions with orbital periods long enough to permit the existence of habitable, Earth-like planets on shorter-period orbits. These stars are generally too faint and red to be included in ground-based Doppler planet surveys, which are often optimized for FGK dwarfs. The smaller masses of late M dwarfs also yield correspondingly larger astrometric signals for a given mass planet. Our search will help to determine whether gas giant planets form primarily by core accretion or by disk instability around late M dwarf stars., Comment: 48 pages, 9 figures. in press, Publ. Astron. Soc. Pacific

We report here the discovery of the first planet around an ultracool dwarf star. It is also the first extrasolar giant planet (EGP) astrometrically discovered around a main-sequence star. The statistical significance of the detection is shown in two ways. First, there is a 2 x 10^-8 probability that the astrometric motion fits a parallax-and-proper-motion-only model. Second, periodogram analysis shows a false alarm probability of 3 x 10^-5 that the discovered period is randomly generated. The planetary mass is M2 = 6.4 (+2.6,-3.1) Jupiter-masses (MJ), and the orbital period is P = 0.744 (+0.013,-0.008) yr in the most likely model. In less likely models, companion masses that are higher than the 13 MJ planetary mass limit are ruled out by past radial velocity measurements unless the system radial velocity is more than twice the current upper limits and the near-periastron orbital phase was never observed. This new planetary system is remarkable, in part, because its star, VB 10, is near the lower mass limit for a star. Our astrometric observations provide a dynamical mass measurement and will in time allow us to confront the theoretical models of formation and evolution of such systems and their members. We thus add to the diversity of planetary systems and to the small number of known M-dwarf planets. Planets such as VB 10b could be the most numerous type of planets because M stars comprise >70% of all stars. To date they have remained hidden since the dominant radial-velocity (RV) planet-discovery technique is relatively insensitive to these dim, red systems., 1 30 page pdf file, 9 figures, accepted for publication in The Astrophysical Journal

Precision astrometry at microarcsecond accuracy has application to a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument that delivers parallaxes at about 4 microarcsec on targets as faint as V = 20, differential accuracy of 0.6 microarcsec on bright targets, and with flexible scheduling. The science topics are drawn primarily from the Team Key Projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase, having completed all of the enabling technologies needed for the flight instrument in 2005. It will be the first space-based long baseline Michelson interferometer designed for precision astrometry. SIM will contribute strongly to many astronomical fields including stellar and galactic astrophysics, planetary systems around nearby stars, and the study of quasar and AGN nuclei. SIM will search for planets with masses as small as an Earth orbiting in the `habitable zone' around the nearest stars using differential astrometry, and could discover many dozen if Earth-like planets are common. It will be the most capable instrument for detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve with time. SIM will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%, the accuracy needed to challenge physical models. Using precision proper motion measurements, SIM will probe the galactic mass distribution and the formation and evolution of the Galactic halo. (abridged), 54 pages, 28 figures, uses emulateapj. Submitted to PASP

Band-limited image plane masks, in conjunction with appropriate Lyot stops, function effectively to suppress host star light while transmitting planet light to the final image for detecting and characterizing faint exo-solar terrestrial planets. In this article, we review various types of image plane masks, their design, fabrication, and characterization. Measured characteristics and performance of sample masks in simulations and in laboratory experiments are also discussed. Star light suppression contrast better than 10−9 in the 4 to 10 λ / D region has been demonstrated with such a mask in our laboratory testbed. To cite this article: K. Balasubramanian et al., C. R. Physique 8 (2007).

“Are we alone in the Universe?” is probably the most compelling science question of our generation. To answer it requires a large aperture telescope with extreme wavefront stability. To image and characterize Earth-like planets requires the ability to block 1010 of the host star’s light with a 10-11 stability. For an internal coronagraph, this requires correcting wavefront errors and keeping that correction stable to a few picometers rms for the duration of the science observation. This requirement places severe specifications upon the performance of the observatory, telescope and primary mirror. A key task of the AMTD project (initiated in FY12) is to define telescope level specifications traceable to science requirements and flow those specifications to the primary mirror. From a systems perspective, probably the most important question is: What is the telescope wavefront stability specification? Previously, we suggested this specification should be 10 picometers per 10 minutes; considered issues of how this specification relates to architecture, i.e. monolithic or segmented primary mirror; and asked whether it was better to have few or many segments. This paper reviews the 10 picometers per 10 minutes specification; provides analysis related to the application of this specification to segmented apertures; and suggests that a 3 or 4 ring segmented aperture is more sensitive to segment rigid body motion that an aperture with fewer or more segments.

The Stellar Planet Survey (STEPS) is an ongoing astrometric search for giant planets and brown dwarfs around a sample of ~30 M-dwarfs. We have discovered several low-mass companions by measuring the motion of our target stars relative to their reference frames. The highest mass discovery thus far is G 78-28B, a companion to the M-dwarf G 78-28A. The orbital period is 4.18 +/- 0.03 y, the system mass is 0.565 +/- 0.055 Msolar, and the semi-major axis is 2.19 +/- 0.10 AU. Imaging observations with the Keck laser guide star adaptive optics (LGSAO) and the Palomar AO instruments resolved the system and also yielded JHK-band delta magnitudes. We use the orbital solution, light ratios, and mass-luminosity relationships to derive component masses of MA = 0.370 +/- 0.034 Msolar and MB = 0.195 +/- 0.021 Msolar. G 78-28B is of type M4 V based upon its colors and mass. We also discovered GJ 231.1C, a companion to GJ 231.1B, with STEPS and imaged the companion with LGSAO and Palomar AO, but the orbital period is longer than our observing baseline; thus the system parameters are less constrained. In GJ 231.1BC the masses are MB = 0.25 +/- 0.06 Msolar and MC =0.12 +/- 0.02 Msolar. The inferred spectral type of GJ 231.1C is M5 V. We demonstrate the results of the current state of mass estimation techniques with our data., 25 pages, 8 figures, accepted for ApJ

Occulting focal plane masks for the Terrestrial Planet Finder Coronagraph (TPF-C) could be designed with continuous gray scale profile of the occulting pattern such as 1-sinc2 on a suitable material or with micron-scale binary transparent and opaque structures of metallic pattern on glass. We have designed, fabricated and tested both kinds of masks. The fundamental characteristics of such masks and initial test results from the High Contrast Imaging Test bed (HCIT) at JPL are presented.

The Stellar Planet Survey is an ongoing astrometric search for giant planets and brown dwarfs around a sample of about 30 M-dwarfs. We have discovered several low-mass companions by measuring the motion of our target stars relative to their reference frames. The lowest mass discovery thus far is GJ 802b, a companion to the M5-dwarf GJ 802A. The orbital period is 3.14 +/- 0.03 y, the system mass is 0.214 +/- 0.045 Msolar, and the semi-major axis is 1.28 +/- 0.10 AU or 81 +/- 6 mas. Imaging observations indicate that GJ 802b is likely to be a brown dwarf with the astrometrically determined mass 0.058 +/- 0.021 Msolar (one sigma limits). The remaining uncertainty in the orbit is the eccentricity that is now loosely constrained. We discuss how the system age limits the mass and the prospects to further narrow the mass range when e is more precisely determined., 13 pages, 6 figures, accepted for publication in ApJ on May 9, 2005

In a recent paper, Kuchner, Crepp, and Ge describe new image-plane coronagraph mask designs that reject to eighth order the leakage of starlight caused by image motion at the mask, resulting in a substantial relaxation of image centroiding requirements compared to previous fourth-order and second-order masks. They also suggest that the new masks are effective at rejecting leakage caused by low-order aberrations (e.g., focus, coma, and astigmatism). In this paper, we derive the sensitivity of eighth-order masks to aberrations of any order and provide simulations of coronagraph behavior in the presence of optical aberrations.We find that the masks leak light as the fourth power of focus, astigmatism, coma, and trefoil. This has tremendous performance advantages for the Terrestrial Planet Finder Coronagraph.

The Space Interferometry Mission (SIM), part of NASA's Origins Program, aims at the detection of planetary systems around distant stars. The astrometric observations of the SIM instrument are performed via high-accuracy path-length measurements with a system of three Michelson-type white-light stellar interferometers. A procedure for on-orbit calibration of the instrument error function is described, along with a proof of the concept's viability. On a given grid of stars, the procedure generates approximations of the gradient of the instrument error function at a discrete set of field points corresponding to the star locations via a specialized set of maneuvers of the spacecraft. These gradient approximations are then used to estimate the error function via a least-squares procedure in a manner that is analogous to the wave-front reconstruction problem in adaptiveoptics systems. An error analysis of the procedure is presented that provides further insights into the connections between instrument errors and the grid reduction solution. Finally, numerical results are presented on a randomly generated grid of stars that demonstrate the feasibility of the method.

In preparation for optical/IR interferometric searches for substellar companions of nearby stars, we undertook to characterize the fields of all nearby stars visible from the Northern Hemisphere to determine suitable companions for interferometric phase referencing. Because the Keck Interferometer in particular will be able to phase-reference on companions within the isoplanatic patch (30'') to about 17th magnitude at K, we took images at V, r, and i that were deep enough to determine if field stars were present to this magnitude around nearby stars using a spot-coated CCD. We report on 733 fields containing 10,629 measurements in up to three filters (Gunn i, r and Johnson V) of nearby stars down to about 13th magnitude at V.

Searching for nearby habitable worlds with direct imaging and spectroscopy will require a telescope large enough to provide angular resolution and sensitivity to planets around a significant sample of stars. Segmented telescopes are a compelling option to obtain such large apertures. However, these telescope designs have a complex geometry (central obstruction, support structures, segmentation) that makes high-contrast imaging more challenging. We are developing a new high-contrast imaging testbed at STScI to provide an integrated solution for wavefront control and starlight suppression on complex aperture geometries. We present our approach for the testbed optical design, which defines the surface requirements for each mirror to minimize the amplitude-induced errors from the propagation of out-of-pupil surfaces. Our approach guarantees that the testbed will not be limited by these Fresnel propagation effects, but only by the aperture geometry. This approach involves iterations between classical ray-tracing optical design optimization, and end-to-end Fresnel propagation with wavefront control (e.g. Electric Field Conjugation / Stroke Minimization). The construction of the testbed is planned to start in late Fall 2013., Proc. of the SPIE 8864, 10 pages, 3 figures, Techniques and Instrumentation for Detection of Exoplanets VI

The design and scale of a future mission to directly image and characterize potentially Earth-like planets will be impacted, to some degree, by the expected yield of such planets. Recent efforts to increase the estimated yields, by creating observation plans optimized for the detection and characterization of Earth-twins, have focused solely on coronagraphic instruments; starshade-based missions could benefit from a similar analysis. Here we explore how to prioritize observations for a starshade given the limiting resources of both fuel and time, present analytic expressions to estimate fuel use, and provide efficient numerical techniques for maximizing the yield of starshades. We implemented these techniques to create an approximate design reference mission code for starshades and used this code to investigate how exoEarth candidate yield responds to changes in mission, instrument, and astrophysical parameters for missions with a single starshade. We find that a starshade mission operates most efficiently somewhere between the fuel- and exposure-time limited regimes, and as a result, is less sensitive to photometric noise sources as well as parameters controlling the photon collection rate in comparison to a coronagraph. We produced optimistic yield curves for starshades, assuming our optimized observation plans are schedulable and future starshades are not thrust-limited. Given these yield curves, detecting and characterizing several dozen exoEarth candidates requires either multiple starshades or an eta_Earth > ~0.3., Accepted for publication in JATIS

The specification of polishing requirements for the optics in coronagraphs dedicated to exo-planet detection requires careful and accurate optical modelling. Numerical representations of the propagation of aberrations through the system as well as simulations of the broadband wavefront compensation system using multiple DMs are critical when one devises an error budget for such a class of instruments. In this communication we introduce an analytical tool that serves this purpose for Phase Induced Amplitude Apodisation (PIAA) coronagraphs. We first start by deriving the analytical form of the propagation of a harmonic ripple through a PIAA unit. Using this result we derive the chromaticity of the field at any plane in the optical train of a telescope equipped with such a coronagraph. Finally we study the chromatic response of a sequential DM wavefront actuator correcting such a corrugated field and thus quantify the requirements on the manufacturing of PIAA mirrors

The high level of spatial uniformity in modern CCD’s makes them excellent devices for astrometric instruments. However, at the level of accuracy envisioned by the more ambitious projects such as the Astrometric Imaging Telescope, current technology produces CCD’s with significant pixel registration errors. We describe a technique for making high-precision measurements of relative pixel positions. We measured CCD’s manufactured for the Wide Field Planetary Camera II installed in the Hubble Space Telescope. These CCD’s are shown to have significant step-and-repeat errors of 0.033 pixel along every 34th row, as well as a 0.003-pixel curvature along 34-pixel stripes. The source of these errors is described. Our experiments achieved a per-pixel accuracy of 0.011 pixel. The ultimate shot-noise limited precision of the method is less than 0.001 pixel.