arXiv subjects

Geoffrey Bryden

Publications and source records attributed to Geoffrey Bryden.

At least 19 recordsLinked to original sources

arXiv2026

The JWST/NIRCam Scattered Light Disks GTO 2780 program: panchromatic coronagraphic imaging of the HD 10647, HD 32297, HD 61005, HD 107146, and HD 181327 debris disk systems

Debris disks, composed of rocks, boulders, planetesimals, and the dust produced in their collisions, present the most readily observable components of mature planetary systems. They also serve as valuable diagnostic tools, enabling studies of planetary dynamical interactions and mineral compositions. Observed from optical to radio wavelengths, each band reveals unique information about the dust populations. Optical and near-infrared observations are specifically sensitive to light scattered off the surfaces of the micron-sized particles. Here, we present results from the JWST/NIRCam GTO program 2780, designed to observe five disk systems previously identified to be exceptionally bright at optical wavelengths (HD 10647, HD 32297, HD 61005, HD 107146, and HD 181327) with six filters using the NIRCam coronagraphs. The NIRCam data complement previous shorter-wavelength images of these same systems. They reveal scattered light from the disks and from the extended halos of tiny grains under the influence of radiative forces, at high resolution and signal to noise. All the systems show evidence for water ice, although it can have differing radial distributions and tends to show stronger signatures in the halos. In the two cases we could analyze, the scattering phase function in the disks resembles the behavior of dust in the Solar System with evidence for enhanced forward scattering in the halos, consistent with the latter being composed of tiny grains. MIRI images for two systems are more centrally concentrated than the shorter wavelength ones, suggesting a role for dragged-in larger grains.

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arXiv2026

Exoplanet System Architecture: Sculpting the Inner Regions

In this study, we seek to improve our understanding of the competing roles of disk-driven and planet-planet dynamical migration in sculpting planetary system architecture in the inner $\lesssim 1.5$ au of protoplanetary disks. Over a range of host star masses, we compare the orbit semimajor axis values of transiting multi-planet and resonant systems to observationally-derived estimates of protoplanetary disk inner truncation radius $R_{i}$, corotation radius $R_{co}$, and dust sublimation radius $R_{dust}$. We find that disk-driven migration is primarily responsible for setting the inner edge of planetary systems near $R_{co}$ and that subsequent dynamical migration shapes the distribution of planetary semimajor axis values over the range $\approx 20-300$ $R_{\star}$. If multi-planet systems form in a way similar to the resonant chain systems, either a zone of highly efficient planet formation at $\gtrsim 100 R_{\star}$, followed by subsequent disk-driven migration, is implied, or a modified in-situ mechanism operating over a region from $\simeq 15-100 R_{\star}$ and incorporating disk-driven migration is needed. There are indications that after disk dispersal, dynamical migration causes a subset of planets to migrate to locations inside $R_{co}$.

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arXiv2026

Comparing Results from Two Uniform Phase Curve Surveys

We present a comparison of the two most recent and comprehensive Spitzer phase curve studies - Dang et al. (2025) and Swain et al. (2025) - which report analyses of the Spitzer 4.5 $\mu$m phase curves. The studies employ different approaches for correcting instrument systematics and they also use different approaches for selecting the optimal exoplanet system parameters. To evaluate the level of consistency between the two studies, we compared the constraints on the ratio of planet-to-star radii ($R_P/R_\star$), eclipse depth ($F_P/F_\star$), phase curve amplitude ($A$), and phase curve offset ($\phi$). We find that the two studies produce similar results at the population level although results for individual planets can vary, especially for phase curve offset values. We examined the difference of planet system parameters to see if inconsistencies in individual planet results were due to data reduction methods or system parameter choices. We also examined whether the system parameters used by both studies were consistent with Kepler's third law. During this comparison, we identified one case where stellar mass, planet semi-major axis, and orbital period did not follow Kepler's law even though the values were all compiled from the same publication. To assess whether this kind of discrepancy was recurrent, we recalculated the orbital periods using Kepler's third law and compared them with the values listed in the NASA Exoplanet Archive. Our detailed analysis of archival system parameters strongly suggests that testing reported/selected parameters for consistency with Kepler's third law is worthwhile.

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arXiv2026

Worlds Next Door. III. Indirect Evidence for Enhanced Atmospheric Metallicity and/or the Presence of Water Clouds in the Nearest Jupiter-analog $\epsilon$ Eri b

We present the most sensitive direct imaging search for the nearest ($d = 3.2$ pc) Jupiter-analog exoplanet, $\epsilon$ Eri b, with JWST/NIRCam coronagraphy between 4-5 $\mu$m (F444W). We achieve a 5$\sigma$ contrast sensitivity $\approx3.0\times10^{-7}$ ($\Delta \approx 16.3$ mag) in the F444W filter at the expected planet separation of $\approx$1". This is the deepest 4-5 $\mu$m contrast performance achieved for any JWST/NIRCam observation to date at these separations (and $>10\times$ better than ground-based limits). Yet, the planet remains elusive to imaging. We update the star's age to $1.1\pm0.1$ Gyr, older than previous age estimates, using the latest gyrochronology relations. This significantly impacts $\epsilon$ Eri b's inferred effective temperature ($T_{\rm eff}$), which is now expected to lie between 150-200 K based on evolutionary models for a 1 $M_{\rm Jup}$ planet. Using cloud-free Sonora Flame Skimmer models and custom PICASO patchy cloud models in the above $T_{\rm eff}$ range, we find that the F444W non-detection of $\epsilon$ Eri b can be explained by a metal-enriched atmosphere and/or an atmosphere containing water ice clouds. Both possibilities suggest that $\epsilon$ Eri b's atmosphere is strikingly similar to that of Jupiter in our Solar System. Alternatively, if we do not enforce the dynamical mass ($0.98 \pm 0.09\;M_{\rm Jup}$), a solar metallicity, cloud-free, $\lesssim0.81\;M_{\rm Jup}$ planet would be consistent with the NIRCam upper limit based on the Sonora Flame Skimmer evolutionary models. Finally, we place limits on the size of a potential ring system using the NIRCam/F210M data and discuss the opportunity to directly image $\epsilon$ Eri b with additional JWST observations, the Roman Coronagraph Instrument, the ExtraSolar Coronagraph on the Lazuli Observatory, and EELT/METIS.

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arXiv2026

The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas

With four giant planets ($m\sim5-10~M_{\rm Jup}$, $T_\rm{eff}\sim900-1200$ K) orbiting between 15-70 au, HR 8799 provides an unparalleled testbed for studying giant planet formation and probing compositional trends across the protoplanetary disk. We present new JWST/NIRSpec IFU observations ($2.85-5.3~\mu$m, $R\approx2700$) that now include the spectrum of HR 8799 b, and higher S/N spectra for HR 8799 c, d, and e compared to that in Ruffio & Xuan et al. We detect CO, CH$_4$, H$_2$O, H$_2$S, CO$_2$, and for planet b, NH$_3$. We combine the NIRSpec spectra with $1-5 \mu$m photometry to perform atmospheric retrievals that account for disequilibrium chemistry and clouds, and allow C/H, O/H, N/H, and S/H to scale independently. While the four planets are similarly enriched in carbon and oxygen, with C/H and O/H between $3-5\times$ stellar, we observe a tentative trend of increasing S/H - a tracer of refractory solids - from $2-5 \times$ stellar with increasing orbital distance. From HR 8799 b's NH$_3$ abundance, we estimate $\rm N/H=21.2^{+16.2}_{-8.8}\times$ stellar, suggesting the outer planet accreted significant amounts of N-rich gas. Overall, the elemental abundance patterns we observe are consistent with a picture where planet b formed between the CO snowline and the more-distant N$_2$ snowline, while the inner planets accreted $3 \times$ stellar CO-enriched disk gas within the CO snowline. The excess volatile mass from pebble drift and evaporation implies an integrated pebble flux of $750 \pm 200~M_{\oplus}$. The increase in the planets' S/H with orbital distance implies more solid accretion further out, which is quantitatively compatible with expectations from both pebble and planetesimal accretion ($2 \times$ Minimum Mass Solar Nebula) paradigms.

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arXiv2026

Jupiter-like uniform metal enrichment in a system of multiple giant exoplanets

The accretion of icy and rocky solids during the formation of a gas giant planet is poorly constrained and challenging to model. Refractory species, like sulfur, are only present in solids in the protoplanetary disk where planets form. Measuring their abundance in planetary atmospheres is one of the most direct ways of constraining the extent and mechanism of solid accretion. Using the unprecedented sensitivity of NASA's James Webb Space Telescope (JWST), we measure a detailed chemical make-up of three massive gas giants orbiting the star HR~8799 including direct detections of H$_2$O, CO, CH$_4$, CO$_2$, H$_2$S, $^{13}$CO, and C$^{18}$O. We find these planets are uniformly and highly enriched in heavy elements compared to the star irrespective of their volatile (carbon and oxygen) or refractory (sulfur) nature, which strongly suggests efficient accretion of solids during their formation. This composition closely resembles that of Jupiter and Saturn and demonstrates that this enrichment also occurs in systems of multiple gas giant planets orbiting stars beyond the Solar System. This discovery hints at a shared origin for the heavy element enrichment of giant planets across a wider range of planet masses and orbital separations than previously anticipated.

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arXiv2025

Roman coronagraph simulations of exozodi observations in the presence of wavefront errors

The Coronagraph Instrument on board of the Nancy Grace Roman Space Telescope will demonstrate key technologies that will prepare the ground for the Habitable Worlds Observatory. The current predictions for the Roman Coronagraph's detection limit range from 1e-8 to a few 1e-9, which would allow for groundbreaking science, such as potentially imaging Jupiter-like planets. However, the performance of the instrument depends on many factors. Simulating images with varying optical error sources can help us connect instrument and observatory performance to science yield. Here we present corosims, a tool to simulate observations of astrophysical scenes with the Coronagraph with evolving errors. This tool wraps around the Coronagraph PROPER diffraction model and detector simulator. We use it to investigate the potential degeneracy between jitter-induced speckles and both hot and warm exozodi disk structures. First, we simulate observations of exozodi around Tau Ceti, with varying jitter. We predict that with nominal post-correction pointing jitter performance (~0.3 mas RMS), the Roman Coronagraph should be sensitive to 12x zodis worth of dust, assuming a face-on (worst case scenario) inclination. We further predict that its sensitivity degrades to 35x zodis if jitter on-target is 3x worse than the nominal value. This estimate assumes the best-modeled wavefront control and stability values from the project, including additional model uncertainty factors. We find that, while jitter hinders warm exozodi detection, jitter residuals are unlikely to result in a false positive. However, if a faint hot exozodi falls at small separation, it may not be distinguishable from jitter-induced speckle residuals of comparable brightness. Finally, we discuss the degeneracies induced between flux and separation retrieved near the inner working angle due the sharp edge of the Roman Coronagraph's focal plane mask.

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arXiv2025

A Near-Infrared Extinction and Reddening Map Towards the Galactic Bulge Using UKIRT

The Galactic bulge is one of the most information-dense regions to study resolved stellar populations, variables, and transients, such as microlensing events. Studies toward the Galactic bulge are complicated by the large and variable extinction along the line of sight. We measure the near-infrared $A_{K_S}$ extinction and $E(H-K_S)$ reddening in this region using $H$- and $K$-band photometry obtained with the 2017 UKIRT microlensing survey. We fit the apparent magnitude and color distribution of bright giants in the bulge to recover the apparent magnitude and color of Red Clump stars, which are known to be standard candles and crayons. We present $2^\prime \times 2^\prime$ resolution maps in UKIRT fields between $-2.15^{\circ} \le l \le 2.71^{\circ}$ and $-2.69^{\circ} \le b \le 2.03^{\circ}$ of the $A_{K_S}$ extinction and the $E(H-K_S)$ reddening. We find large variations in the $K_S$-band extinction and $E(H-K_S)$ reddening on all the scales we probe. We find that a constant, standard extinction law is a poor representation of the relationship between the extinction and reddening we measure in fields of different latitudes. These maps will be useful for understanding the near-infrared extinction law for sight lines close to the Galactic plane, as well as for final field selection for the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey.

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arXiv2025

Searching for Planets Orbiting $\epsilon$~Eridani with JWST/NIRCam

We present observations of \epseri~with the JWST/NIRCam coronagraph aimed at imaging planets orbiting within this system. In particular, these observations targeted (1) the Jupiter-like planet, first detected orbiting at 3.5 AU with radial velocity observations, and (2) the planet postulated to be responsible for carving the edges of \epseri's outer ring, expected to orbit at 40-50 AU. However, no point sources were detected at a statistically significant level. We report new, improved upper limits at 4 $\mu$m: $\sim$1e-7~contrast at 1\arcsec, and $\sim$2e-8~beyond 5\arcsec. The latter contrast limit precludes Saturn-mass planets at separations $>$16~AU given current models. We also report upper limits for \epseri's disk emission at 4 $\mu$m. While the radial surface brightness profile shows no evidence of emission, we detect a 1-$\sigma$ surface brightness signal on the east side of the system, consistent with forward scattering emission expected for \epseri's disk inclination. Finally, we evaluate the performance of the 3-roll observation strategy, which was first employed in these observations: the gains in contrast are modest, with 20-30\% improvements with respect to the conventional 2-roll strategy.

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arXiv2025

A New Approach to Compiling Exoatmospheric Target Lists And Quantifying the Ground-Based Resources Needed to Vet Them

Transiting exoplanet atmospheric characterization is currently in a golden age as dozens of exoplanet atmospheres are being studied by NASA's Hubble and James Webb Space Telescopes. This trend is expected to continue with NASA's Pandora Smallsat and Roman Space Telescope and ESA's Ariel mission (all expected to launch within this decade) and NASA's Habitable Worlds Observatory (expected to launch in the early 2040s) all of which are centered around studying the atmospheres of exoplanets. Here we explore a new approach to constructing large scale exoatmospheric survey lists, which combines the use of traditional transmission/emission spectroscopy figures of merit with a focus on more-evenly sampling planets across a range of radii and equilibrium temperatures. After assembling a sample target list comprised of 750 transmission spectroscopy targets and 150 emission spectroscopy targets, we quantify the potential time lost to stale transit and eclipse ephemerides and find that hundreds of hours of space-based observing could be wasted given current uncertainties in orbital periods, transit epochs, and orbital eccentricities. We further estimate the amount of ground-based telescope time necessary to obtain sufficiently precise exoplanet masses and find that it exceeds 100 nights of 10m telescope time. Based upon these findings, we provide a list of recommendations that would make community efforts for preparation and interpretation of atmospheric characterization endeavors more effective and efficient. The strategies we recommend here can be used to support both current (e.g., HST and JWST) and future exoplanet atmosphere characterization missions (e.g., Pandora, Ariel, Roman, and the Habitable Worlds Observatory).

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arXiv2025

Probing the Outskirts of M Dwarf Planetary Systems with a Cycle 1 JWST NIRCam Coronagraphy Survey

The population of giant planets on wide orbits around low-mass M dwarf stars is poorly understood, but the unprecedented sensitivity of JWST NIRCam coronagraphic imaging now provides direct access to planets significantly less massive than Jupiter beyond 10 AU around the closest, youngest M dwarfs. We present the design, observations, and results of JWST GTO Program 1184, a Cycle 1 NIRCam coronagraphic imaging survey of 9 very nearby and young low-mass stars at 3-5 micron wavelengths. In the F356W and F444W filters, we achieve survey median 5-sigma contrasts deeper than 10-5 at a separation of 1", corresponding to 0.20 MJup in F444W and 1.30 MJup in F356W at planet-star separations of 10 AU. Our results include 3-5 micron debris disk detections and the identification of many extended and point-like sources in the final post-processed images. In particular, we have identified two marginal point source candidates having fluxes and color limits consistent with model predictions for young sub-Jupiter mass exoplanets. Under the assumption that neither candidate is confirmed, we place the first direct-imaging occurrence constraints on M dwarf wide-orbit (semimajor axes 10-100 AU), sub-Jupiter mass exoplanets (0.3-1 MJup). We find frequency limits of < 0.10 and < 0.16 objects per star with 1 and 3-sigma confidence, respectively. This survey brings to the forefront the unprecedented capabilities of JWST NIRCam coronagraphic imaging when targeting young, low-mass stars and acts as a precursor to broader surveys to place deep statistical constraints on wide-orbit, sub-Jupiter mass planets around M dwarfs.

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arXiv2025

JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO$_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres

High-contrast observations with JWST can reveal key composition and vertical mixing dependent absorption features in the spectra of directly imaged planets across the 3-5 $\mu$m wavelength range. We present novel coronagraphic images of the HR 8799 and 51 Eri planetary systems using the NIRCam Long Wavelength Bar in an offset "narrow" position. These observations have revealed the four known gas giant planets encircling HR 8799, even at spatial separations challenging for a 6.5 m telescope in the mid-infrared, including the first ever detection of HR 8799 e at 4.6 $\mu$m. The chosen filters constrain the strength of CO, CH4, and CO2 absorption in each planet's photosphere. The planets display a diversity of 3-5 $\mu$m colors that could be due to differences in composition and ultimately be used to trace their formation history. They also show stronger CO2 absorption than expected from solar metallicity models, indicating that they are metal enriched. We detected 51 Eri b at 4.1 $\mu$m and not at longer wavelengths, which, given the planet's temperature, is indicative of out-of-equilibrium carbon chemistry and an enhanced metallicity. Updated orbits fit to the new measurement of 51 Eri b validate previous studies that find a preference for high eccentricities ($e{=}0.57_{-0.09}^{+0.03}$), which likely indicates some dynamical processing in the system's past. These results present an exciting opportunity to model the atmospheres and formation histories of these planets in more detail in the near future, and are complementary to future higher-resolution, continuum-subtracted JWST spectroscopy.

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arXiv2025

Thermal Phase Curves in Hot Gas Giant Exoplanets Exhibit a Complex Dependence on Planetary Properties

We present a catalog of uniformly processed 3.6-$\mu$m and 4.5-$\mu$m band exoplanet thermal phase curves based on Infrared Array Camera observations obtained from the Spitzer Heritage Archive. The catalog includes phase curve measurements for 34 planets, 16 of which contain full orbit coverage and have detectable secondary eclipses in both channels. The data are processed in the EXCALIBUR pipeline using a uniform analysis consisting of aperture photometry and modeling of instrument effects along with the exoplanet signal. Nearest-neighbors regression with a Gaussian kernel is used to correct for instrumental systematics correlated to the star's centroid position and shape in conjunction with a novel test to avoid overfitting. These methods may have utility in addressing sub-pixel gain variations present in modern infrared detectors. We analyze the 3.6-$\mu$m and 4.5-$\mu$m phase curve properties and find a strong wavelength-dependent difference in how the properties correlate with physical parameters as well as evidence that the phase curve properties are determined by multiple physical parameters. We suggest that differences between the 3.6-$\mu$m and 4.5-$\mu$m phase curve properties are due to 3.6~$\mu$m observations probing regions of the atmosphere which could include a cloud layer. Taken together, the observed phase curve behavior suggests that different physical processes are responsible for establishing the thermal phase curve at different pressures, which are probed by different wavelengths, and that further 3D GCM modeling is required to investigate the reason for this complex dependence on planetary properties.

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arXiv2024

Searching for Planets Orbiting Vega with the James Webb Space Telescope

The most prominent of the IRAS debris disk systems, $\alpha$ Lyrae (Vega), at a distance of 7.7 pc, has been observed by both the NIRCam and MIRI instruments on the James Webb Space Telescope (JWST). This paper describes NIRCam coronagraphic observations which have achieved F444W contrast levels of 3$\times10^{-7}$ at 1\arcsec\ (7.7 au), 1$\times10^{-7}$ at 2\arcsec\ (15 au) and few $\times 10^{-8}$ beyond 5\arcsec\ (38 au), corresponding to masses of $<$ 3, 2 and 0.5 MJup for a system age of 700 Myr. Two F444W objects are identified in the outer MIRI debris disk, around 48 au. One of these is detected by MIRI, appears to be extended and has a spectral energy distribution similar to those of distant extragalactic sources. The second one also appears extended in the NIRCam data suggestive of an extragalactic nature.The NIRCam limits within the inner disk (1\arcsec\ --10\arcsec) correspond to a model-dependent masses of 2$\sim$3 \mj. \citet{Su2024} argue that planets larger even 0.3 MJup would disrupt the smooth disk structure seen at MIRI wavelengths. Eight additional objects are found within 60\arcsec\ of Vega, but none has astrometric properties or colors consistent with planet candidates. These observations reach a level consistent with expected Jeans Mass limits. Deeper observations achieving contrast levels $<10^{-8}$ outside of $\sim$4\arcsec\ and reaching masses below that of Saturn are possible, but may not reveal a large population of new objects.

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arXiv2024

JWST/NIRCam Detection of the Fomalhaut C Debris Disk in Scattered Light

Observations of debris disks offer important insights into the formation and evolution of planetary systems. Though M dwarfs make up approximately 80% of nearby stars, very few M-dwarf debris disks have been studied in detail -- making it unclear how or if the information gleaned from studying debris disks around more massive stars extends to the more abundant M dwarf systems. We report the first scattered-light detection of the debris disk around the M4 star Fomalhaut C using JWST's Near Infrared Camera (NIRCam; 3.6$~\mu$m and 4.4$~\mu$m). This result adds to the prior sample of only four M-dwarf debris disks with detections in scattered light, and marks the latest spectral type and oldest star among them. The size and orientation of the disk in these data are generally consistent with the prior ALMA sub-mm detection. Though no companions are identified, these data provide strong constraints on their presence -- with sensitivity sufficient to recover sub-Saturn mass objects in the vicinity of the disk. This result illustrates the unique capability of JWST for uncovering elusive M-dwarf debris disks in scattered light, and lays the groundwork for deeper studies of such objects in the 2--5$~\mu$m regime.

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arXiv2023

Retrievals of Protoplanetary Disk Parameters using Thermochemical Models: I. Disk Gas Mass from Hydrogen Deuteride Spectroscopy

We discuss statistical relationships between the mass of protoplanetary disks and the hydrogen deuteride (HD) line emission and the dust spectral energy distribution (SED) determined using 3000 ProDiMo disk models. The models have 15 free parameters describing disk physical properties, the central star, and the local radiation field. The sampling of physical parameters is done using a Monte Carlo approach to evaluate the probability density functions of observables as a function of physical parameters. We find that the HD fractional abundance is almost constant even though the UV flux varies by several orders of magnitude. Probing the statistical relation between the physical quantities and the HD flux, we find that low-mass (optically thin) disks display a tight correlation between the average disk gas temperature and HD line flux, while massive disks show no such correlation. We demonstrate that the central star luminosity, disk size, dust size distribution, and HD flux may be used to determine the disk gas mass to within a factor of three. We also find that the far-IR and sub-mm/mm SEDs and the HD flux may serve as strong constraints for determining the disk gas mass to within a factor of two. If the HD lines are fully spectrally resolved ($R\gtrsim 1.5\times10^6, \Delta v=0.2~\rm km\,s^{-1}$), the 56 $\mu$m and 112 $\mu$m HD line profiles alone may constrain the disk gas mass to within a factor of two.

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arXiv2023

Searching for Planets Orbiting Fomalhaut with JWST/NIRCam

We report observations with the JWST/NIRCam coronagraph of the Fomalhaut system. This nearby A star hosts a complex debris disk system discovered by the IRAS satellite. Observations in F444W and F356W filters using the round 430R mask achieve a contrast ratio of ~ 4 x 10-7 at 1'' and ~ 4 x 10-8 outside of 3''. These observations reach a sensitivity limit <1 MJup across most of the disk region. Consistent with the hypothesis that Fomalhaut b is not a massive planet but is a dust cloud from a planetesimal collision, we do not detect it in either F356W or F444W (the latter band where a Jovian-sized planet should be bright). We have reliably detected 10 sources in and around Fomalhaut and its debris disk, all but one of which are coincident with Keck or HST sources seen in earlier coronagraphic imaging; we show them to be background objects, including the "Great Dust Cloud" identified in MIRI data. However, one of the objects, located at the edge of the inner dust disk seen in the MIRI images, has no obvious counterpart in imaging at earlier epochs and has a relatively red [F356W]-[F444W]>0.7 mag (Vega) color. Whether this object is a background galaxy, brown dwarf, or a Jovian mass planet in the Fomalhaut system will be determined by an approved Cycle 2 follow-up program. Finally, we set upper limits to any scattered light from the outer ring, placing a weak limit on the dust albedo at F356W and F444W.

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arXiv2023

JWST-TST High Contrast: Achieving direct spectroscopy of faint substellar companions next to bright stars with the NIRSpec IFU

The JWST NIRSpec integral field unit (IFU) presents a unique opportunity to observe directly imaged exoplanets from 3-5 um at moderate spectral resolution (R~2,700) and thereby better constrain the composition, disequilibrium chemistry, and cloud properties of their atmospheres. In this work, we present the first NIRSpec IFU high-contrast observations of a substellar companion that requires starlight suppression techniques. We develop specific data reduction strategies to study faint companions around bright stars, and assess the performance of NIRSpec at high contrast. First, we demonstrate an approach to forward model the companion signal and the starlight directly in the detector images, which mitigates the effects of NIRSpec's spatial undersampling. We demonstrate a sensitivity to planets that are 3e-6 fainter than their stars at 1'', or 3e-5 at 0.3''. Then, we implement a reference star point spread function (PSF) subtraction and a spectral extraction that does not require spatially and spectrally regularly sampled spectral cubes. This allows us to extract a moderate resolution (R~2,700) spectrum of the faint T-dwarf companion HD 19467 B from 2.9-5.2 um with signal-to-noise ratio (S/N)~10 per resolution element. Across this wavelength range, HD~19467~B has a flux ratio varying between 1e-5-1e-4 and a separation relative to its star of 1.6''. A companion paper by Hoch et al. more deeply analyzes the atmospheric properties of this companion based on the extracted spectrum. Using the methods developed here, NIRSpec's sensitivity may enable direct detection and spectral characterization of relatively old (~1 Gyr), cool (~250 K), and closely separated (~3-5 au) exoplanets that are less massive than Jupiter.

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