arXiv subjects

Sarah Steiger

Publications and source records attributed to Sarah Steiger.

At least 19 recordsLinked to original sources

arXiv2026

JWST telemetry combined with active coronagraphy: raw contrast predictions for exoplanet imaging with the Habitable Worlds Observatory

We provide a quantification of the technological gap between the James Webb Space Telescope (JWST) and the Habitable Worlds Observatory (HWO) for the goal of exo-Earth imaging around Sun-like stars at the $10^{-10}$ raw contrast level. We use JWST's in-flight telemetry of the primary segmented mirror to simulate a JWST-like telescope equipped with a modern coronagraph instrument, inspired by the Roman Space Telescope (RST) Coronagraphic Instrument (CGI), featuring an Apodized Pupil Lyot Coronagraph and active deformable mirror wavefront control on a segmented, unobstructed, off-axis telescope. We show that it can achieve around $10^{-10}$ raw contrast for very bright stars (brighter than magnitude 4) for fast control frequencies of 100 Hz, but that this level of control still lacks sufficient signal to correct JWST-amplitude errors for fainter stars. We show that an improvement of a factor of ten in wavefront stability is sufficient to extend this capability to a $10^{-10}$ raw contrast across all considered control frequencies (1 Hz to 100 Hz), assuming no reaction wheel vibrations, for stars up to a magnitude of 11. These results establish a new quantitative benchmark linking JWST's demonstrated thermo-mechanical stability to HWO's requirements, showing that active wavefront control relaxes the structural stability demands on the observatory, and identifying wavefront stability as the critical technological gap that must be closed for HWO to achieve its exo-Earth imaging goals.

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arXiv2026

pyEDITH: the coronagraphic exposure time calculator for the Habitable Worlds Observatory

To support the development of next-generation missions for the search and characterization of habitable planets, high-fidelity tools for astrophysical and instrumental noise simulations are needed. In this paper, we introduce pyEDITH, the Python-based coronagraphic exposure time calculator built for the next recommended NASA flagship mission, the Habitable Worlds Observatory (HWO), tasked with searching for signs of habitability and life in dozens of nearby exoplanet systems. pyEDITH is designed to simulate wavelength-dependent exposure times and signal-to-noise ratios (S/N) for synthetic HWO direct imaging observations, considering realistic engineering specifications and user-defined target information. Its modular architecture ensures flexibility as mission requirements evolve. pyEDITH enables a streamlined integration with modern astronomical workflows and was designed to be used by the scientific community at all skill levels for understanding the capabilities and limitations of different HWO architectures for exoplanet analyses. The code has been validated against existing exposure time calculators and released open-source on GitHub and Zenodo, as well as made accessible through a Graphical User Interface. The pyEDITH package includes API documentation, tutorial notebooks, and has been used in forthcoming scientific publications.

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arXiv2026

Calibration of MEMS DM actuator gains using a Zernike wavefront sensor on the HiCAT testbed and implications for Habitable Worlds Observatory operations

Deformable mirrors (DMs) are a key component of coronagraph instruments performing adaptive optics on the ground, and for future space observatories such as HWO and Roman CGI. Here, they will be used as part of the wavefront sensing and control system to "dig a dark zone'' - remove residual stellar light to create a high-contrast region in the focal plane where faint companions can be detected. To reach the deep contrasts needed to directly image cool or reflected light planets (<1e-8) accurate calibration of the DM actuator gain is essential as picometer differences between the expected and realized DM surface can significantly degrade dark zone (DZ) digging efficiency. This increases the overheads needed to achieve a DZ and critically places more stringent requirements on observatory stability. Furthermore, DM gain varies with actuator stroke, necessitating rapid, in situ gain map recalculations to maintain DZ digging efficiency over time. Zernike wavefront sensors (ZWFS) are well-suited for this task as they efficiently provide picometer-level sensitivity and will likely already be included on board as part of a low order wavefront sensor for HWO. Here we present results from the HiCAT testbed at STScI where we calibrated gain maps for our Boston Micromachines 952-actuator micro electromechanical (MEMS) DMs using both a Fizeau interferometer and a ZWFS to compare performance. With the ZWFS we compute a gain map using both local linear fits around a given DM solution, and present a formalism for deriving more complex quadratic solutions which are more computationally intensive, but accurate over most of the dynamic range of each actuator. We then use these techniques to calibrate the DMs on the HiCAT testbed and show increased DZ digging efficiency with the new gain map and better contrast performance moving from 14 to 16 bit control electronics as enabled by these calibrations.

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arXiv2026

CATKit2-HCI: a collaborative framework for advancing high-contrast coronagraph testbeds

High-contrast exoplanet imaging requires dedicated laboratory testbeds for the development and validation of coronagraph architectures, wavefront sensing and control methods, calibration strategies, and system-level observing concepts. These testbeds often share similar software needs, yet many tools are developed independently at each institution. The CATKit2-High-Contrast-Imaging collaboration, or CATKit2-HCI, addresses this gap by providing a shared software framework for reusable HCI infrastructure. Built on top of CATKit2, an open-source hardware control and synchronization framework originally developed for the High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed at the Space Telescope Science Institute, CATKit2-HCI provides the collaborative layer for HCI-specific algorithms, calibration tools, diagnostics, visualization, and performance metrics. The collaboration currently includes multiple coronagraph testbeds in the United States and Europe. Its goals are to reduce duplicated software development, improve code quality through shared review, enable more direct comparison of results across facilities, and facilitate the movement of students, postdoctoral researchers, and collaborators between laboratories. We describe the motivation, architecture, collaboration model, shared technical capabilities, and early cross-testbed examples of CATKit2-HCI as a framework for accelerating coronagraph technology development.

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arXiv2026

Impact of segmented deformable mirrors on high-contrast testbeds for exoplanet imaging with future large space telescopes: contrast stability assessment on the HiCAT bench

We investigate the stability of a segmented deformable mirror (DM) on high-contrast testbeds and its impact on the images produced with coronagraphs. Segmented apertures are promising to obtain large primary mirrors for future missions with starlight suppression capabilities. Cophased at the sub-nanometer level, segments can be slightly misaligned by small drifts, proving harmful for exoplanet observations. We study the impact of misalignments on contrast using the High-contrast Imager for Complex Aperture Telescopes (HiCAT), a testbed which includes a 37-segment DM and produces coronagraphic images with 2.5e-8 contrast in narrowband light. Temporal wavefront errors due to the segmented DM are estimated with a Zernike wavefront sensor. Our in-lab results show aberrations at the sub-nanometer level, proving encouraging for contrast stability studies. We then use a digital twin of HiCAT to simulate coronagraphic images with an initial 0.5e-8 contrast and the segments in flat position. By injecting known perturbations on the segments, we observe a contrast degradation by a factor of 2.5, nearly corresponding to the typical contrast observed on HiCAT. These results highlight the importance of segment cophasing sensing and control strategies to ensure the required contrasts for exo-Earth imaging with a large segmented aperture for the Habitable Worlds Observatory mission.

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arXiv2026

Characterizing Earth analogs may require a moderate or high-resolution spectrograph

A primary goal of the Habitable Worlds Observatory (HWO) is to detect and measure the abundance of biosignature molecules, such as water (H2O) and oxygen (O2), in the atmosphere of Earth analogs. This is expected to require deep spectroscopic observations lasting hundreds of hours per planet. In this context, it is essential to optimize the spectral resolution of the spectrograph to both maximize the number of planets that can be studied over the lifetime of the mission, and also to reduce the risks of false detections. The purpose of this work is to provide a framework to explore the spectral resolution design trade-space for HWO. This framework must be valid and comparable across all spectral resolutions from low (R<100) to high resolutions (R>10,000), and account for the spectral correlation of the residual starlight (i.e., speckle noise chromaticity). Leveraging the concept of "template matching", we develop a simulation toolkit based on the Python package EXOSIMS to compute the detection significance of planets and molecules. We then simulate observations of Earth analogs around 164 stars using representative mission parameters to explore the effects of the detector noise and the correlated speckle noise floor. Our findings suggest that a moderate or high resolution spectrograph (R>1,000) will provide higher sensitivity to critical molecules compared to a low resolution spectroscopy mode (e.g., R~140). The correlated speckle noise may also entirely suppress our ability to detect bio-signatures at low spectral resolutions. We conclude that a more comprehensive study combined with detailed models of its stability, and other sources of correlated noise, is necessary to fully explore the trade space of spectral resolution and detectability of key species.

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arXiv2026

Incorporating Wavefront Error, Wavefront Sensing and Control, and Sensitivities into Exposure Time Calculations for Future Space Missions with the Error Budget Software (EBS)

A primary goal of NASA's Habitable Worlds Observatory (HWO) mission concept is to explore the Habitable Zones (HZ) of ~100 stellar systems and acquire spectra of ~25 terrestrial-type planets (with planet/star flux ratios on the order of 1E-10) which places tight constraints on the performance of observatory systems. In particular, coronagraph instrumentation needs to be matured for higher throughput, deeper contrasts, and better broadband performance, while also considering their sensitivity and ability to mitigate the impact of telescope instability and wavefront error (WFE), which can have a profound impact on exo-Earth imaging. The success of various proposed HWO mission architectures is often represented by the estimated exo-Earth candidate yield. Computation of the minimum exposure time to achieve the required signal-to-noise on a given target, using an exposure time calculator (ETC), is a key part of yield estimation. The impacts of coronagraph sensitivity, WFE, and wavefront sensing and control (WFS&C) have been well studied in the context of developing error budgets for missions and instruments such as the Roman Coronagraph Instrument, but there is currently no easily accessible way to incorporate the effects of these key parameters into calculating exposure times for HWO. To address this, we developed the Error Budget Software (EBS) - an open-source tool that synthesizes sensitivity, WFE, and WFS&C information for a variety of temporal and spatial scales and directly interfaces with the open-source yield code EXOSIMS to produce exposure times. We demonstrate how EBS can be used for mission error budgeting using the example of the Ultrastable Observatory Roadmap Team (USORT) observatory design. This includes both single and multi-variate parameter explorations using EBS where we identify trends between raw contrast and wavefront error, and detector noise and energy resolution.

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arXiv2025

yieldplotlib: A unified library for exoplanet yield code visualizations

NASA's next flagship observatory, the Habitable Worlds Observatory (HWO), aims to detect and charaterize ~25 habitable zone planets. The total number of habitable zone planets detected is referred to as the exo-Earth "yield'' and accurate yield estimates will be critically important to the mission's success. Tools like the Altruistic Yield Optimizer (AYO) and EXOSIMS provide these yield estimates but differ in language, methods, and outputs. yieldplotlib provides a unified library that can visualize the inputs and outputs of these yield codes in a complete, descriptive, and accessible way.

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arXiv2025

Cross-Model Validation of Coronagraphic Exposure Time Calculators for the Habitable Worlds Observatory: A Report from the Exoplanet Science Yield sub-Working Group

Estimating the exoplanet scientific productivity of the Habitable Worlds Observatory requires estimating science exposure times. From exoplanet yields to spectral retrievals, exposure times are at the heart of our understanding of the capabilities of this future mission. As such, ensuring accuracy and consistency between different exposure time calculators (ETCs) is critical. We summarize the efforts of the Exoplanet Science Yield sub-Working Group's ETC Calibration Task Group, which conducted a calibration study from March 4 to June 30 of 2024. We compare three commonly-used coronagraphic exposure time calculators. We find that the ETCs use a broad variety of differing methods, assumptions, and inputs that produce variation in the final exposure times at the ~60% level. The causes for the disagreement have largely been identified, flagged for further development efforts, and in some cases retired since the conclusion of this effort. We expect that addressing the flagged efforts will bring the ETCs to within better than ~30% agreement.

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arXiv2024

High-contrast imager for complex aperture telescopes (HiCAT): 11. System-level demonstration of the Apodized Pupil Lyot Coronagraph with a segmented aperture in air

We present the final results of the Apodized Pupil Lyot Coronagraph (APLC) on the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed, under NASA's Strategic Astrophysics Technology program. The HiCAT testbed was developed over the past decade to enable a system-level demonstration of coronagraphy for exoplanet direct imaging with the future Habitable Wolds Observatory. HiCAT includes an active, segmented telescope simulator, a coronagraph, and metrology systems (Low-order and Mid-Order Zernike Wavefront Sensors, and Phase Retrieval camera). These results correspond to an off-axis (un-obscured) configuration, as was envisioned in the 2020 Decadal Survey Recommendations. Narrowband and broadband dark holes are generated using two continuous deformable mirrors (DM) to control high order wavefront aberrations, and low-order drifts can be further stabilized using the LOWFS loop. The APLC apodizers, manufactured using carbon nanotubes, were optimized for broadband performance and include the calibrated geometric aperture. HiCAT is, to this date, the only testbed facility able to demonstrate high-contrast coronagraphy with a truly segmented aperture, as is required for the Habitable World Observatory, albeit limited to ambient conditions. Results presented here include $6\times 10^{-8}$ (90% CI) contrast in 9% bandpass in a 360 deg dark hole with inner and outer working angles of $4.4 \lambda/D_{pupil}$ and $11 \lambda/D_{pupil}$ . Narrowband contrast (3% bandpass) reaches $2.4\times 10^{-8}$ (90% confidence interval).

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arXiv2024

Simulated performance of energy-resolving detectors towards exoplanet imaging with the Habitable Worlds Observatory

One of the primary science goals of the Habitable Worlds Observatory (HWO) as defined by the Astro2020 decadal survey is the imaging of the first Earth-like planet around a Sun-like star. A key technology gap towards reaching this goal are the development of ultra-low-noise photon counting detectors capable of measuring the incredibly low count rates coming from these planets which are at contrasts of $\sim 1 \times 10^{-10}$. Superconducting energy-resolving detectors (ERDs) are a promising technology for this purpose as, despite their technological challenges, needing to be cooled below their superconducting transition temperature ($< 1\mathrm{K}$), they have essentially zero read noise, dark current, or clock-induced charge, and can get the wavelength of each incident photon without the use of additional throughput-reducing filters or gratings that spread light over many pixels. The use of these detectors on HWO will not only impact the science of the mission by decreasing the required exposure times for exo-Earth detection and characterization, but also in a wavefront sensing and control context when used for starlight suppression to generate a dark zone. We show simulated results using both an EMCCD and an ERD to ``dig a dark zone'' demonstrating that ERDs can achieve the same final contrast as an EMCCD in about half of the total time. We also perform a simple case study using an exposure time calculator tool called the Error Budget Software (EBS) to determine the required integration times to detect water for HWO targets of interest using both EMCCDs and ERDs. This shows that once a dark zone is achieved, using an ERD can decrease these exposure times by factors of 1.5--2 depending on the specific host star properties.

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arXiv2024

Current laboratory performance of starlight suppression systems, and potential pathways to desired Habitable Worlds Observatory exoplanet science capabilities

We summarize the current best polychromatic (10 to 20 % bandwidth) contrast performance demonstrated in the laboratory by different starlight suppression approaches and systems designed to directly characterize exoplanets around nearby stars. We present results obtained by internal coronagraph and external starshade experimental testbeds using entrance apertures equivalent to off-axis or on-axis telescopes, either monolithic or segmented. For a given angular separation and spectral bandwidth, the performance of each starlight suppression system is characterized by the values of raw contrast (before image processing), off-axis (exoplanet) core throughput, and post-calibration contrast (the final 1 sigma detection limit of off-axis point sources, after image processing). To place the current laboratory results in the perspective of the future Habitable Worlds Observatory (HWO) mission, we simulate visible observations of a fiducial Earth/Sun twin system at 12 pc, assuming a 6m (inscribed diameter) collecting aperture and a realistic end-to-end optical throughput. The exposure times required for broadband exoearth detection (20% bandwidth around a wavelength of 0.55 microns) and visible spectroscopic observations (R=70) are then computed assuming various levels of starlight suppression performance, including the values currently demonstrated in the laboratory. Using spectroscopic exposure time as a simple metric, our results point to key starlight suppression system design performance improvements and trades to be conducted in support of HWO exoplanet science capabilities. These trades may be explored via numerical studies, lab experiments, as well as high contrast space-based observations and demonstrations.

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arXiv2022

Probing Photon Statistics in Adaptive Optics Images with SCExAO/MEC

We present an experimental study of photon statistics for high-contrast imaging with the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera (MEC) located behind the Subaru Coronagraphic Extreme Adaptive Optics System (SCExAO) at the Subaru Telescope. We show that MEC measures the expected distributions for both on-axis companion intensity and off-axis intensity which manifests as quasi-static speckles in the image plane and currently limits high-contrast imaging performance. These statistics can be probed by any MEC observation due to the photon-counting capabilities of MKID detectors. Photon arrival time statistics can also be used to directly distinguish companions from speckles using a post-processing technique called Stochastic Speckle Discrimination (SSD). Here, we we give an overview of the SSD technique and highlight the first demonstration of SSD on an extended source -- the protoplanetary disk AB Aurigae. We then present simulations that provide an in-depth exploration as to the current limitations of an extension of the SSD technique called Photon-Counting SSD (PCSSD) to provide a path forward for transitioning PCSSD from simulations to on-sky results. We end with a discussion of how to further improve the efficacy of such arrival time based post-processing techniques applicable to both MKIDs, as well as other high speed astronomical cameras.

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arXiv2022

SCExAO and Keck Direct Imaging Discovery of a Low-Mass Companion Around the Accelerating F5 Star HIP 5319

We present the direct imaging discovery of a low-mass companion to the nearby accelerating F star, HIP 5319, using SCExAO coupled with the CHARIS, VAMPIRES, and MEC instruments in addition to Keck/NIRC2 imaging. CHARIS $JHK$ (1.1-2.4 $\mu$m) spectroscopic data combined with VAMPIRES 750 nm, MEC $Y$, and NIRC2 $L_{\rm p}$ photometry is best matched by an M3--M7 object with an effective temperature of T=3200 K and surface gravity log($g$)=5.5. Using the relative astrometry for HIP 5319 B from CHARIS and NIRC2 and absolute astrometry for the primary from $Gaia$ and $Hipparcos$ and adopting a log-normal prior assumption for the companion mass, we measure a dynamical mass for HIP 5319 B of $31^{+35}_{-11}M_{\rm J}$, a semimajor axis of $18.6^{+10}_{-4.1}$ au, an inclination of $69.4^{+5.6}_{-15}$ degrees, and an eccentricity of $0.42^{+0.39}_{-0.29}$. However, using an alternate prior for our dynamical model yields a much higher mass of 128$^{+127}_{-88}M_{\rm J}$. Using data taken with the LCOGT NRES instrument we also show that the primary HIP 5319 A is a single star in contrast to previous characterizations of the system as a spectroscopic binary. This work underscores the importance of assumed priors in dynamical models for companions detected with imaging and astrometry and the need to have an updated inventory of system measurements.

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arXiv2022

The MKID Science Data Pipeline

We present The MKID Pipeline, a general use science data pipeline for the reduction and analysis of ultraviolet, optical and infrared (UVOIR) Microwave Kinetic Inductance Detector (MKID) data sets. This paper provides an introduction to the nature of MKID data sets, an overview of the calibration steps included in the pipeline, and an introduction to the implementation of the software.

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arXiv2021

SCExAO/MEC and CHARIS Discovery of a Low Mass, 6 AU-Separation Companion to HIP 109427 using Stochastic Speckle Discrimination and High-Contrast Spectroscopy

We report the direct imaging discovery of a low-mass companion to the nearby accelerating A star, HIP 109427, with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument coupled with the MKID Exoplanet Camera (MEC) and CHARIS integral field spectrograph. CHARIS data reduced with reference star PSF subtraction yield 1.1-2.4 $\mu$m spectra. MEC reveals the companion in $Y$ and $J$ band at a comparable signal-to-noise ratio using stochastic speckle discrimination, with no PSF subtraction techniques. Combined with complementary follow-up $L_{\rm p}$ photometry from Keck/NIRC2, the SCExAO data favors a spectral type, effective temperature, and luminosity of M4-M5.5, 3000-3200 $K$, and $\log_{10}(L/L_{\rm \odot}) = -2.28^{+0.04}_{-0.04}$, respectively. Relative astrometry of HIP 109427 B from SCExAO/CHARIS and Keck/NIRC2, and complementary Gaia-Hipparcos absolute astrometry of the primary favor a semimajor axis of $6.55^{+3.0}_{-0.48}$ au, an eccentricity of $0.54^{+0.28}_{-0.15}$, an inclination of $66.7^{+8.5}_{-14}$ degrees, and a dynamical mass of $0.280^{+0.18}_{-0.059}$ $M_{\odot}$. This work shows the potential for extreme AO systems to utilize speckle statistics in addition to widely-used post-processing methods to directly image faint companions to nearby stars near the telescope diffraction limit.

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arXiv2020

Improving the dynamic range of single photon counting kinetic inductance detectors

We develop a simple coordinate transformation which can be employed to compensate for the nonlinearity introduced by a Microwave Kinetic Inductance Detector's (MKID) homodyne readout scheme. This coordinate system is compared to the canonically used polar coordinates and is shown to improve the performance of the filtering method often used to estimate a photon's energy. For a detector where the coordinate nonlinearity is primarily responsible for limiting its resolving power, this technique leads to increased dynamic range, which we show by applying the transformation to data from a hafnium MKID designed to be sensitive to photons with wavelengths in the 800 to 1300 nm range. The new coordinates allow the detector to resolve photons with wavelengths down to 400 nm, raising the resolving power at that wavelength from 6.8 to 17.

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arXiv2020

The MKID Exoplanet Camera for Subaru SCExAO

We present the MKID Exoplanet Camera (MEC), a z through J band (800 - 1400 nm) integral field spectrograph located behind The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) at the Subaru Telescope on Maunakea that utilizes Microwave Kinetic Inductance Detectors (MKIDs) as the enabling technology for high contrast imaging. MEC is the first permanently deployed near-infrared MKID instrument and is designed to operate both as an IFU, and as a focal plane wavefront sensor in a multi-kHz feedback loop with SCExAO. The read noise free, fast time domain information attainable by MKIDs allows for the direct probing of fast speckle fluctuations that currently limit the performance of most high contrast imaging systems on the ground and will help MEC achieve its ultimate goal of reaching contrasts of $10^{-7}$ at 2$\lambda / D$. Here we outline the instrument details of MEC including the hardware, firmware, and data reduction and analysis pipeline. We then discuss MEC's current on-sky performance and end with future upgrades and plans.

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