arXiv subjects

Thayne Currie

Publications and source records attributed to Thayne Currie.

At least 19 recordsLinked to original sources

arXiv2026

SCExAO/CHARIS High-Contrast Pre-Launch Vetting of Roman Coronagraph Technology Demonstration PSF Reference Stars

We present deep, SCExAO/CHARIS high-contrast integral field spectroscopy and archival imaging of four candidate Roman Coronagraph PSF reference stars within/near the Roman Continuous Viewing Zone and potentially suitable for the Coronagraph's key technology demonstration targets HIP 71618 and HIP 54515. For CHARIS data, we achieve 5-$\sigma$ contrasts down to $\sim$1.4$\times$10$^{-5}$, $\sim$6$\times$10$^{-6}$, and 10$^{-6}$ to 4$\times$10$^{-7}$ at 0\farcs{}16, 0\farcs{}25, and 0\farcs{}5 to 1\arcsec{}. Companion mass limits rule out brown dwarfs at $\rho$ $\sim$ 0\farcs{}15--0\farcs{}25 and massive planets at wider separations around all targets. More critically, for three of the four references our analysis disfavors companions with $V$ band contrasts brighter than 10$^{-8}$, 10$^{-9}$, and $10^{-10}$ at 0\farcs{}15, 0\farcs{}3, and 1$\arcsec{}$. Unless these targets have faint substellar companions within $\rho$ $\sim$ 0\farcs{}15, they likely lack background stars or companions that could corrupt the Roman Coronagraph's dark hole digging to preclude detecting reflected-light planets. For $\alpha$ Cep, our limits are a factor of $\sim$10 worse but still meet the TTR5 limit of 10$^{-7}$ beyond $\rho$ $\sim$ 0\farcs{}25: beyond 0\farcs{}4, they exclude a Jupiter-twin reflected-light companion (10$^{-9}$). Archival Keck/NIRC2 data likewise find no substellar companions with $\Delta$V $>$ 10$^{-8}$ at wider separations. Finally, we assess the observability of HIP 71618 and HIP 54515 -- updated for Roman's launch date of August 30, 2026. Adding $\gamma$ Boo -- not currently in the Roman CPP team reference-star list -- would improve schedulability for the tech demo's key targets.

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arXiv2026

Technology and Science Advancing Observations with Roman Coronagraph Informed by Ground-Based High-Contrast Imaging

The Roman Coronagraph technology demonstration focuses on achieving $<$ 10$^{-7}$ contrasts within the instrument's dark hole and our ability to detect and characterize properties of faint companions around bright stars. Here, we describe results from a study of potential Roman Coronagraph technology demonstration phase observations focused on these goals, informed by the ongoing OASIS survey at the Subaru Telescope and precursor survey work. OASIS provides at least three compelling targets for the technology demonstration phase with imaged companions - the HIP 71618 B brown dwarf and superjovian planets HIP 54515 b and HIP 99770 b. HIP 71618 is well suited for demonstrating the Coronagraph's core performance requirement while all three targets are well suited for spectroscopic mode observations. Each target can be paired with a PSF reference star vetted for companions. While HIP 71618 and HIP 54515 are already planned for Technology Demonstration phase observations, we describe the programmatic and scientific value of adding spectroscopic mode observations of HIP 99770 as well.

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arXiv2026

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems VIII: patchy forsterite and enstatite clouds in the atmosphere of VHS 1256 b, retrieval lessons learned and outlook to the future

JWST defines a new era for the data-driven approach of retrieval modelling, which has become a cornerstone tool for the statistical inference of exoplanetary and brown dwarf properties. The Early Release Science program #1386 observations of VHS 1256 b represent a huge jump in data quality, data quantity and spectral coverage for such objects. VHS 1256 b is a young, planetary mass and extremely variable companion that populates the enigmatic L/T cohort of substellar atmospheres. In this first retrieval analysis of the full 1 - 18 micron dataset, we apply the Brewster retrieval framework to the NIRSpec and MIRI spectroscopic observations of VHS 1256 b, exploring a variety of cloud species and structures. Using Delta(BIC) we find that the data is best described by a forsterite (Mg$_{2}$SiO$_{4}$) and enstatite (MgSiO$_{3}$) cloud combination. Our analysis shows a strong preference for patchy silicate cloud coverage, which aligns with VHS 1256 b's extensive and well documented spectral variability. Our retrieval is able to place constraints on the abundances of H$_{2}$O, CO, CO$_{2}$, CH$_{4}$ as well as NH$_{3}$. We also show that the retrieved parameters are sensitive to the data used and the relative signal-to-noise ratios between data from different instruments. We conclude with the next steps for the wider retrieval community to better understand young and cloudy exoplanetary atmospheres.

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arXiv2026

FIRST-PL: Commissioning the first visible photonic lantern spectrograph for sub-diffraction-limit astronomy on Subaru/SCExAO

FIRST-PL (Fibered Imager foR a Single Telescope - Photonic Lantern) is a newly commissioned visible-light instrument on Subaru/SCExAO achieving spectroscopy below the diffraction limit. The instrument uses a Photonic Lantern (PL)-converting multimode fiber into 19 single-mode outputs-feeding a mid-resolution spectrograph (R 3000, 630-790 nm). On-sky performance demonstrates 40% injection efficiency at 680 nm (Strehl 30%) and 12x throughput improvement over single-mode fibers. Three operational modes enable spectro-astrometry (50 microarcseconds precision demonstrated on beta-CMi), image reconstruction, and high-contrast imaging. FIRST-PL represents a significant advancement in high-throughput photonic instrumentation.

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arXiv2026

Updating the SCExAO/CHARIS polarimetric calibration following the Nasmyth beam-switcher upgrade

Subaru/SCExAO/CHARIS enables near-infrared integral field spectropolarimetry. Quantitative polarimetry is useful for a variety of science cases, particularly measurements related to dust grain properties in circumstellar disks. This capability requires correcting for polarization effects from the optical path via a Mueller matrix model. We present an updated model accounting for the recently installed SCExAO near-infrared wavefront sensor YJH50 dichroic beamsplitter and the major Subaru Nasmyth beam-switcher upgrade. Using internal light source measurements from before and after the beam switcher installation, we find an elliptical retarder model for the image derotator improves polarimetric accuracy over the previous linear retarder model. We additionally find the YJH50 dichroic produces faint polarization effects that we cannot characterize with our Mueller matrix modeling capabilities, and that the Nasmyth beam-switcher has minimal polarization effects other than inducing a sign flip in Q and V polarized light. Using unpolarized standard star calibration measurements, we fit the diattenuation of Subaru's tertiary mirror as a function of wavelength and find that the diattenuation has increased since the previous CHARIS calibration. We calculate that the polarimetric accuracy of the model in the degree of linear polarization ranges from 0.02% to 0.12% for a 1% polarized target. This model update will soon be incorporated into CHARIS's data processing pipeline, and should be used for any polarimetric data taken after the Nasmyth beam-switcher update in October 2025. Additionally, we provide the code for this calibration as part of an open-source Python package for polarimetric calibration called pyPolCal, enabling straightforward re-calibration of the system after any future changes, e.g. the recent recoating of M3.

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arXiv2026

Combining spectroscopy and wavefront control at deep contrast with photonic lanterns

HWO aims to directly image objects orbiting Sun-like stars, using a 6-m telescope capable of high-contrast imaging ($10^{-10}$) and spectroscopy to search for biosignatures in planets located in the habitable zone. Recent laboratory demonstrations and ground-based telescope projects have shown the effectiveness of SMFs in spectroscopy, paving the way for SMF-fed spectrographs in future space missions like HWO. SMFs enhance spectral stability and reduce modal noise. HWO spectroscopy will need extended integration times, potentially lasting weeks. During these observations, the wavefront must be precisely measured and maintained to achieve the deep contrast and robust calibration of starlight contamination necessary for exoplanet characterization. We show that photonic lanterns (PLs) are ideally suited to meet these requirements. PLs are compact devices that couple light over a broader angular range than SMFs, ensuring higher throughput, converting a multimode input into multiple single-mode outputs. Positioned at the focal plane, they measure the complex amplitude of the coherent starlight within $\sim$ 2 l/D of the planet image, acting as compact wavefront sensors. Among the different variants of PLs that have emerged, the Hybrid-Mode Selective Photonic Lantern (HMSPL) is particularly attractive, as it directs object light into a central SMF feeding a mid-R spectrograph for exoplanet spectroscopy, while the adjacent SMFs route surrounding speckle light to a low-R spectrograph for rapid wavefront sensing. This dual function eliminates non-common path aberrations, optimizing injection efficiency and background suppression. We introduce HMSPL's dual role and planned tests at UTSA's high-contrast imaging lab and at SCExAO at the Subaru Telescope.

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arXiv2026

Discovery of a Low-Mass Companion to the Accelerating Star HIP 53005 with Strongly Conflicting Mass Estimates

We present the discovery of a low-mass companion located at $\rho$ $\sim$ 0\farcs{}85 ($r_{\rm proj} \approx 62~au$) from the early-type 1.2 Gyr-old star HIP 53005 using direct imaging data from the Subaru and Keck Telescopes and astrometry from the Hipparcos-Gaia Catalog of Accelerations. The companion, HIP 53005 C, is a component of a multiple system also including a $\approx$ 12\farcs{}4-separation M dwarf companion inducing a negligible proper motion acceleration. HIP~53005 C's position on color-magnitude diagrams, the fit of its spectral energy distribution to atmosphere models, and its location on an empirical mass-magnitude diagram all suggest that it lies at the M/L transition and near the hydrogen-burning limit ($\sim80~M_{\rm Jup}$). However, our orbital fitting combining direct-imaging relative astrometry with proper motion acceleration favors a much higher dynamical mass of $\sim185\ M_{\rm Jup}$. An additional unseen, more closely-orbiting companion below the detection limit (at $\rho\lesssim0\farcs2$)) may explain this discrepancy. Alternatively, HIP~53005C could be a low-mass binary like Gliese~229Bab, making this system an intriguing laboratory for studying multiple star formation.

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arXiv2026

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. VII. Molecular Mapping Performance with JWST/MIRI MRS: VHS 1256 b as a case study

VHS 1256 b was the first planetary-mass companion to be observed with the James Webb Space Telescope's Mid-Infrared Instrument (JWST/MIRI) using the Medium-Resolution Spectrometer (MRS). The MRS provides high-quality integral-field spectral data in the mid-infrared (IR) wavelengths from 4.9 to 18 um. This dataset serves as a testbed for applying cross-correlation techniques to characterize exoplanet atmospheres. We implement the so-called molecular mapping approach, which consists of performing a spectral cross-correlation between each spectral pixel and atmospheric model templates. We compare these results with those obtained from cross-correlation of the extracted spectrum. Using a self-consistent Exo-REM atmospheric model grid, we constrain the temperature, surface gravity, C/O ratio, and metallicity, finding values consistent with those obtained from other analysis methods. We detect CO (S/N $\sim$ 25) and H2O (S/N $\sim$ 76), with tentative detections of NH3 and CH4 (S/N$\sim$ 3). We test cross-correlation to measure trace-species abundances and isotopic ratios. We measure a volume mixing ratio of [NH3] =-5.73^{+0.15}_{-0.14} and an isotopic ratio $^{12}\mathrm{C}/^{13}\mathrm{C}=77.8^{+13}_{-10}$, both consistent with free-chemistry retrievals. The derived NH3 volume mixing ratio, combined with the measured temperature and radius, is consistent with VHS 1256 b having a mass above the deuterium-burning limit. These results demonstrate the diagnostic power of mid-IR spectroscopy and highlight cross-correlation as a robust method for characterizing directly imaged exoplanets, even in future higher-contrast regimes where spectral extraction becomes challenging. Future MIRI MRS observations across a wider range of temperatures and masses will further expand our understanding of planetary atmospheric chemistry.

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arXiv2026

A Roman Coronagraph Spectroscopic Mode Demonstration

We propose 730 nm high-contrast spectroscopic observations of selected self-luminous directly-imaged planets as a key test of the Roman Coronagraph's planet characterization capabilities. The planet sample draws from ground-based IR discoveries with the NASA headquarters-supported Subaru/OASIS survey -- HIP 99770 b and HIP 54515 b -- and ``emblematic" planets $\beta$ Pic b and HR 8799 e. All of these planets are likely unsuitable for achieving the coronagraph's core TTR5 goal at 575 nm but are detectable at longer wavelength passbands. Their predicted contrasts at 730 $\mu m$ cover two orders of magnitude range; all companions reside within the dark hole region enabled by the shaped-pupil coronagraph at 730 nm. These observations will help to fulfill multiple Coronagraph Objectives, providing a first assessment of the wavelength dependence of speckle noise and the ability to extract accurate atmospheric information in the face of this noise. Additionally, they will provide a first experiment at extracting optical planet spectra in the face of signal contamination from a debris disk: prefiguring challenges that the Habitable Worlds Observatory may encounter with imaging Earths in exozodi-contaminated systems.

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arXiv2025

Decisively Demonstrating Roman CGI's TTR5 Requirement by Reimaging a Newly-Discovered Brown Dwarf Orbiting a Bright Accelerating Star

We propose Roman Coronagraph project HLC/575 nm observations of a newly-discovered brown dwarf (HIP 71618 B) from the Subaru/OASIS survey of young accelerating stars, which is supported by NASA headquarters with the directive to identify targets for the Roman Coronagraph that could fulfill TTR5 requirements and be observed during the technology demonstration phase. The target and multiple bright PSF references are within/close to the Roman Continuous Viewing Zone. A high SNR detection of this companion would singlehandedly fulfill TTR5 and would be the first optical detection of a companion at $<$10$^{-6}$ contrast. Roman CPP reference star vetting prioritizing stars that can be paired with HIP 71618 would aid the execution of a successful technology demonstration. Additional similar targets may be discovered from OASIS over the next few years that could increase CGI scheduling flexibility and enhance its scientific and technical return. A close collaborative partnership with the CPP team could ensure that they are schedulable.

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arXiv2025

The HIP 54515 b Superjovian Planet as an Early, Critical Look at the Roman Coronagraph's Performance in the Faint Target Star, Small IWA Limit

The Roman Coronagraph's capabilities in the faint star, small IWA limit has enormous scientific (programmatic) impacts. Testing its performance in this limit provides a first look at challenges that may be encountered with the Habitable Worlds Observatory in imaging rocky planets around the nearest K and M stars. We propose such a rigorous test with the HLC/575nm targeting a newly-discovered superjovian planet HIP 54515 b, whose predicted contrast is $\sim$4.7 $\times$10$^{-8}$--2.5 $\times$10$^{-7}$. The companion lies close to the coronagraph IWA (well interior to the TTR5 performance region) and orbits a V = 6.8 star, near the limit for which the coronagraph may yield deep contrasts. Multiple reference stars are available that will further test CGI's performance as a function of $\Delta$ pitch angle to assess how the telescope's thermal environment impacts contrasts.

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arXiv2025

SCExAO/CHARIS and Gaia Direct Imaging and Astrometric Discovery of a Superjovian Planet 3--4 lambda/D from the Accelerating Star HIP 54515

We present the discovery of a superjovian planet around the young A5 star HIP 54515, detected using precision astrometry from the Hipparcos Gaia Catalogue of Accelerations and high-contrast imaging with SCExAO/CHARIS from the recently-commenced OASIS program. SCExAO/CHARIS detects HIP 54515 b in five epochs 0\farcs{}145--0\farcs{}192 from the star ($\sim$3--4 $\lambda$/D at 1.65 $\mu m$), exhibiting clockwise orbital motion. HIP 54515 b lies near the M/L transition with a luminosity of log(L/L$_{\rm \odot}$) $\sim$ -3.52 $\pm$ 0.03. Dynamical modeling constrains its mass and mass ratio to be ${17.7}_{-4.9}^{+7.6}$ $M_{\rm Jup}$ and ${0.0090}_{-0.0024}^{+0.0036}$ and favors a $\sim$25 au semimajor axis. HIP 54515 b adds to a growing list of superjovian planets with moderate eccentricities (e $\approx$ 0.4). Now the third planet discovered from surveys combining high-contrast extreme adaptive optics imaging with precision astrometry, HIP 54515 b should help improve empirical constraints on the luminosity evolution and eccentricity distribution of the most massive planets. It may also provide a key technical test of the Roman Space Telescope Coronagraph Instrument's performance in the low stellar flux, small angular separation limit and a demonstration of its ability to yield constrainable planet spectral properties.

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arXiv2025

OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration

We present the OASIS survey program discovery of a substellar companion orbiting the young A1V star HIP 71618, detected using precision astrometry from Gaia and Hipparcos and high-contrast imaging with SCExAO/CHARIS and Keck/NIRC2. Atmospheric modeling favors a spectral type of M5--M8 and a temperature of $\sim$2700 $\pm$ 100 $K$. Dynamical modeling constrains HIP 71618 B's mass to be ${60}_{-21}^{+27}$ $M_{\rm Jup}$ or ${65}_{-29}^{+54}$ $M_{\rm Jup}$, depending on the adopted companion mass prior. It has a nearly edge-on, 11 au-orbit with a high eccentricity. HIP 71618 B will be located within Roman Coronagraph's dark hole region during the instrument's technological demonstration phase. A high signal-to-noise ratio detection of HIP 71618 B at 575 nm would demonstrate a 5-$\sigma$ contrast of 10$^{-7}$ or better. The system is also located within or very close to Roman's Continuous Viewing Zone -- near multiple candidate reference stars for dark-hole digging -- and its primary is bright ($V$ $\approx$ 5). The suitability of HIP 71618 as one potential Roman Coronagraph target for demonstrating the instrument's core requirement (TTR5) should motivate the timely, deep vetting of candidate reference stars.

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arXiv2025

Dynamical Analysis of the HD 169142 Planet-Forming Disk: Twelve Years of High-Contrast Polarimetry

We present a dynamical analysis of the HD 169142 planet-forming disk based on high-contrast polarimetric imaging over a twelve-year observational period, offering insights into its disk evolution and planet-disk interactions. This study explores the evolution of scattered-light features and their relationship with millimeter continuum emission. Archival visible-to-near-infrared scattered-light observations from NACO, SPHERE, and GPI combined with new observations from SCExAO reveal persistent non-axisymmetric structures in both the inner and outer rings of the disk. Through Keplerian image transformations and phase cross-correlation techniques, we show that the azimuthal brightness variations in the inner ring follow the local Keplerian velocity, suggesting these are intrinsic disk features rather than planet-induced spirals or shadows. The motion of the outer ring is weakly detected, requiring a longer observational baseline for further confirmation. Comparing scattered-light features with ALMA 1.3 mm-continuum data, we find that the scattered light traces the edges of dust structures in the inner ring, indicating complex interactions and a leaky dust trap around the water-ice snowline. These findings highlight the capability of long-term monitoring of circumstellar disks to distinguish planetary influences from Keplerian disk dynamics.

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arXiv2025

Demonstrating Improved Contrast on the Roman Coronagraph with Spatial Linear Dark Field Control

The baseline contrast floor from the Roman Coronagraph's High-Order Wavefront Sensing and Control strategy likely degrades over the course of time, requiring periodic recalibration of the dark hole. Here, we propose to consider spatial linear dark field control (sLDFC) on a one-sided deep-contrast region of the focal plane as a potential test. Implementing sLDFC on CGI will likely require some unique data acquisition strategies given the EMCCD's high flux sensitivity in long exposures/high gain: we outline three possible approaches. However, if successful, sLDFC's advances are substantial: (1) enabling us to maintain a fainter, more temporally correlated dark hole which will improve CGI's contrast after post-processing and (2) efficiently providing a reliable signal (bright field) for accurate reconstruction of residual starlight in the dark field, further boosting CGI's detection limit for bright targets.

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arXiv2025

Multi-band Spectral and Astrometric Characterization of the HIP 99770 b Planet with SCExAO/CHARIS and Gaia

We present and analyze follow-up, higher resolution ($R$ $\sim$ 70) $H$ and $K$ band integral field spectroscopy of the superjovian exoplanet HIP 99770 b with SCExAO/CHARIS. Our new data recover the companion at a high signal-to-noise ratio in both bandpasses and more than double the astrometric baseline for its orbital motion. Jointly modeling HIP 99770 b's position and the star's astrometry from Hipparcos and Gaia yields orbital parameters consistent with those from the discovery paper, albeit with smaller errors, and a slight preference for a smaller semimajor axis ($\sim$15.7--15.8 au)and a larger eccentricity ($\sim$0.28--0.29), disfavoring a circular orbit. We revise its dynamical mass slightly downwards to 15.0$_{-4.4}^{+4.5}$ $M_{\rm Jup}$ for a flat prior and 13.1$_{-5.2}^{+4.8}$ $M_{\rm Jup}$ for a more standard log-uniform mass prior, where the inclusion of its relative radial-velocity measurement is primarily responsible for these changes. We find consistent results for HIP 99770 b's dynamical mass including recent VLTI/GRAVITY astrometry, albeit with a slightly smaller, better constrained eccentricity of $e$ $\sim$ 0.22$^{+0.10}_{-0.13}$. HIP 99770 b is a $\sim$ 1300 K object at the L/T transition with a gravity intermediate between that of the HR 8799 planets and older, more massive field brown dwarfs with similar temperatures but with hints of equilibrium chemistry. HIP 99770 b is particularly well suited for spectroscopic follow up with Roman CGI during the technology demonstration phase at 730 nm to further constrain its metallicity and chemistry; JWST thermal infrared observations could likewise explore the planet's carbon chemistry, metallicity, and clouds.

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arXiv2025

A Striking First Impression: CGI Commissioning Observations of the AB Aurigae Protoplanetary System

For one of the first set of Roman Coronagraph project images, we propose to target AB Aurigae. AB Aurigae is a complex and visually stunning system, surrounded by a gas rich protoplanetary disk showing numerous spiral arms, an enigmatic embedded protoplanet (AB Aurigae b) at 0\farcs{}6 separation, and hints of potential additional sites of planet formation. Even a marginally-successful dark hole generation (e.g. 10$^{-5}$--10$^{-6}$ contrast) with CGI would yield a vastly improved view of AB Aur b at optical wavelengths where current ground-based and HST data struggle to yield a high SNR detection and parameters (astrometry, photometry) unbiased by processing artifacts. Total intensity imaging and polarimetry together will provide new constraints on the disk's dust properties and the range of emission sources for AB Aur b. AB Aur images with the Roman Coronagraph will provide a striking, inspiring demonstrations of the instrument's power and promise for detecting fainter planets and disks.

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arXiv2025

VLT/MUSE Detection of the AB Aurigae b Protoplanet with $H _{\rm \alpha}$ Spectroscopy

We analyze high-contrast, medium-spectral-resolution $H_{\rm \alpha}$ observations of the star AB Aurigae using the Very Large Telescope's Multi Unit Spectroscopic Explorer (MUSE). In multiple epochs, MUSE detects the AB Aur b protoplanet discovered from Subaru/SCExAO data in emission at wavelengths slightly blue-shifted from the $H_{\rm \alpha}$ line center (i.e. at 6558.88--6560.13 \AA; $\sim$ -100 km s$^{-1}$) and in absorption at redshifted wavelengths (6562.8--6565.1 \AA; $\sim$ 75 km s$^{-1}$). AB Aur b's $H_{\rm \alpha}$ spectrum is inconsistent with that of the host star or the average residual disk spectrum and is dissimilar to that of PDS 70 b and c. Instead, the spectrum's shape resembles that of an inverse P Cygni profile seen in some accreting T Tauri stars and interpreted as evidence of infalling cold gas from accretion, although we cannot formally rule out all other nonaccretion origins for AB Aur b's MUSE detection. AB Aurigae hosts only the second protoplanetary system detected in $H_{\rm \alpha}$ thus far and the first with a source showing a spectrum resembling an inverse P Cygni profile. Future modeling and new optical data will be needed to assess how much of AB Aur b's emission source(s) originates from protoplanet accretion reprocessed by the disk, a localized scattered-light feature with a unique $H_{\rm \alpha}$ profile, or another mechanism.

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