arXiv subjects

S. K. Leggett

Publications and source records attributed to S. K. Leggett.

At least 19 recordsLinked to original sources

arXiv2026

The Y Dwarf Companion to the White Dwarf WD 0806-66: Resolving the Discrepancy Between Atmospheric and Evolutionary Models

James Webb Space Telescope near- and mid-infrared spectroscopy has been published by Voyer et al. (2025) and Lew et al. (2026) for the Y dwarf which is a distant companion to the white dwarf WD 0806-661 (Luhman et al. 2011). This target is important because the distance and the age of the system are well constrained by the primary star. Voyer et al. perform a retrieval analysis of the longer wavelength MIRI data, and Lew et al. perform retrieval and forward model grid analyses of the NIRSpec data. These studies produce different results, and both are discrepant with evolutionary model calculations based on the age of the system and the luminosity of the Y dwarf. Here we confirm the luminosity of the Y dwarf, and update the age of the system to 1.6 +0.6 -0.4 Gyr. We compare the combined NIRSpec and MIRI dataset to synthetic spectra generated by ATMO 2020++ atmospheric models. We find a good fit across the entire observed spectral energy distribution, except at the shortest near-infrared wavelengths, with atmospheric parameters consistent with evolutionary models. We find the Y dwarf to be slightly metal-poor, with an effective temperature of 357 +/- 3 K, a radius of 1.08 +/- 0.02 R_Jupiter, and a mass of 7 +/- 1 M_Jupiter.

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arXiv2026

The Coldest Known Y Dwarfs: Estimates of their Effective Temperatures

For a decade there has been a factor of 2.5 gap in luminosity between the 275K WISE J085510.83-071442.5 (Luhman 2014) and all other Y dwarfs, with Teff >= 350K. Recently three objects were found which may fall in this gap. Two are companions to Y dwarfs: WISE J033605.05-014350.4B (Calissendorff et al. 2023) and CWISEP J193518.58-154620.3B (De Furio et al. 2025); the third is MEAD 62B, a candidate companion to a white dwarf (Albert et al. 2025). Evolutionary models calculate a tight relationship between luminosity and Teff for Y dwarfs. I determine luminosities and hence Teff for three Y dwarfs (WISE J085510.83-071442.5, WISE J173835.53+273259.0, WISE J182831.08+265037.7). I derive relationships between Teff and mid-infrared colors using these together with 22 T and Y dwarfs from Beiler et al. (2024) with luminosity-based Teff values. These relationships are used to explore the Teff distribution for Y dwarfs. A sample of 31 Y dwarfs within ~20 pc is presented with 275 < Teff K < 425. The JWST colors for WISE J053516.80-750024.9 and WISE J182831.08+265037.7 support previous suggestions that they are unresolved binaries, the former a 480K and 340K dwarf pair and the latter a pair of 387K dwarfs. Five other dwarfs have unusual colors; two are likely high gravity and/or metal-poor (WISE J024714.52+372523.5, WISEA J215949.54-480855.2), two low gravity and/or metal-rich (CWISEP J104756.81+545741.6, WISE J150115.92-400418.4), and the fifth cannot be interpreted (WISE J043052.92+463331.6). An Appendix provides colors which can be used as a reference for searches for brown dwarfs in JWST data.

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arXiv2025

Exploration of the Near-Infrared Colors of Cold Y Dwarfs from the Ground and Space

JWST has provided critical mid-infrared data for cold brown dwarfs. It has also provided low-resolution near-infrared spectra, and for faint sources these are the first spectra at these wavelengths. We use these data and other literature sources to synthesize near-infrared photometry on the MKO system for 19 T and Y dwarfs, on the Euclid system for 44 T and Y dwarfs, and on the Roman system for 48 T and Y dwarfs. We also synthesize Euclid I_E magnitudes for 15 T and Y dwarfs. Using the Beiler et al. 2024 observational effective temperatures (T_eff), together with ATMO 2020++ model colors, we show that the absolute 4.6um magnitude can be used as a proxy for T_eff. We present a polynomial fit to the M_W2:T_eff relationship for cool dwarfs with 250 < T_eff K < 1000. We select five Y dwarfs with 275 < T_eff K < 400 which have a range in near- to mid-infrared colors. Comparison of the JWST spectral energy distribution to ATMO 2020++ models indicate that Y dwarfs which are bluer in J - W2 are lower gravity or more metal-rich than their redder counterparts, with stronger CO and CO_2 absorption at 4.2 < lambda um < 4.9. The near-infrared color diagrams show significant scatter, with complex dependencies on T_eff, metallicity and gravity. In order to disentangle these effects, opacity sources for cool model atmospheres need to be more complete at lambda < 1um.

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arXiv2025

Redshifting the Study of Cold Brown Dwarfs and Exoplanets: the Mid-Infrared Wavelength Region as an Indicator of Surface Gravity and Mass

JWST is opening many avenues for exploration. For cold brown dwarfs and exoplanets, JWST has opened the door to the mid-infrared wavelength region, where such objects emit significant energy. For the first time, astronomers have access to mid-infrared spectroscopy for objects colder than 600 K. The first spectra appear to validate the model suite known as ATMO 2020++: atmospheres which include disequilibrium chemistry and have a non-adiabatic pressure-temperature relationship. Preliminary fits to JWST spectroscopy of Y dwarfs show that the slope of the energy distribution from lambda = 4.5 um to lambda = 10 um is very sensitive to gravity. We explore this phenomenon using PH3-free ATMO 2020++ models and updated WISE W2 - W3 colors. We find that an absolute 4.5 um flux measurement constrains temperature, and the ratio of the 4.5 um flux to the 10 - 15 um flux is sensitive to gravity and less sensitive to metallicity. We identify 10 T dwarfs with red W2 - W3 colors which are likely to be very low gravity, young, few-Jupiter-mass objects; one of these is the previously known COCONUTS-2b. The unusual Y dwarf WISEPA J182831.08+265037.8 is blue in W2 - W3 and we find that the 4 to 18 um JWST spectrum is well reproduced if the system is a pair of high gravity 400 K dwarfs. Recently published JWST colors and luminosity-based effective temperatures for late-T and Y dwarfs further corroborate the ATMO 2020++ models, demonstrating the potential for significant improvement in our understanding of cold very low-mass bodies in the solar neighborhood.

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arXiv2023

The First Y Dwarf Data From JWST Show That Dynamic and Diabatic Processes Regulate Cold Brown Dwarf Atmospheres

The James Webb Space Telescope (JWST) is now observing Y dwarfs, the coldest known brown dwarfs, with effective temperatures T_eff <= 475 K. The first published observations provide important information: not only is the atmospheric chemistry out of equilibrium, as previously known, but the pressure-temperature profile is not in the standard adiabatic form. The rapid rotation of these Jupiter-size, isolated, brown dwarfs dominates the atmospheric dynamics, and thermal and compositional changes disrupt convection. These processes produce a colder lower atmosphere, and a warmer upper atmosphere, compared to a standard adiabatic profile. Leggett et al. (2021) presented empirical models where the pressure-temperature profile was adjusted so that synthetic spectra reproduced the 1 <= lambda um <= 20 spectral energy distributions of brown dwarfs with 260 <= T_eff K <= 540. We show that spectra generated by these models fit the first JWST Y dwarf spectrum better than standard-adiabat models. Unexpectedly, there is no 4.3 um PH_3 feature in the JWST spectrum and atmospheres without phosphorus better reproduce the 4 um flux peak. Our analysis of new JWST photometry indicates that the recently discovered faint secondary of the WISE J033605.05-014350AB system (Calissendorff et al. 2023) has T_eff = 295 K, making it the first dwarf in the significant luminosity gap between the 260 K WISE J085510.83-071442.5, and all other known Y dwarfs. The adiabat-adjusted disequilibrium-chemistry models are recommended for analyses of all brown dwarfs cooler than 600 K, and a grid is publicly available. Photometric color transformations are provided in an Appendix.

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arXiv2023

Disk or Companion: Characterizing Excess Infrared Flux in Seven White Dwarf Systems with Near-Infrared Spectroscopy

Excess infrared flux from white dwarf stars is likely to arise from a dusty debris disk or a cool companion. In this work, we present near-infrared spectroscopic observations with Keck/MOSFIRE, Gemini/GNIRS, and Gemini/Flamingos-2 of seven white dwarfs with infrared excesses identified in previous studies. We confirmed the presence of dust disks around four white dwarfs (Gaia J0611-6931, Gaia J0006+2858, Gaia J2100+2122, and WD 0145+234) as well as two new white dwarf brown dwarf pairs (Gaia J0052+4505 and Gaia J0603+4518). In three of the dust disk systems, we detected for the first time near-infrared metal emissions (Mg I, Fe I, and Si I) from a gaseous component of the disk. We developed a new Markov Chain Monte Carlo framework to constrain the geometric properties of each dust disk. In three systems, the dust disk and the gas disk appear to coincide spatially. For the two brown dwarf white dwarf pairs, we identified broad molecular absorption features typically seen in L dwarfs. The origin of the infrared excess around Gaia J0723+6301 remains a mystery. Our study underlines how near-infrared spectroscopy can be used to determine sources of infrared excess around white dwarfs, which has now been detected in hundreds of systems photometrically.

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arXiv2023

Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs

Mapping out the populations of thick disk and halo brown dwarfs is important for understanding the metallicity dependence of low-temperature atmospheres and the substellar mass function. Recently, a new population of cold and metal-poor brown dwarfs has been discovered, with $T_{\rm{eff}}$ $\lesssim$ 1400 K and metallicity $\lesssim$ $-$1 dex. This population includes what may be the first known "extreme T-type subdwarfs" and possibly the first Y-type subdwarf, WISEA J153429.75$-$104303.3. We have conducted a Gemini YJHK/Ks photometric follow-up campaign targeting potentially metal-poor T and Y dwarfs, utilizing the GNIRS and Flamingos-2 instruments. We present 14 near-infrared photometric detections of 8 unique targets: six T subdwarf candidates, one moderately metal poor Y dwarf candidate, and one Y subdwarf candidate. We have obtained the first ever ground-based detection of the highly anomalous object WISEA J153429.75$-$104303.3. The F110W$-$$J$ color of WISEA J153429.75$-$104303.3 is significantly bluer than that of other late-T and Y dwarfs, indicating that WISEA J153429.75$-$104303.3 has an unusual spectrum in the 0.9-1.4 $μ$m wavelength range which encompasses the $J$-band peak. Our $J$-band detection of WISEA J153429.75$-$104303.3 and corresponding model comparisons suggest a subsolar metallicity and temperature of 400-550 K for this object. JWST spectroscopic follow-up at near-infrared and mid-infrared wavelengths would allow us to better understand the spectral peculiarities of WISEA J153429.75$-$104303.3, assess its physical properties, and conclusively determine whether or not it is the first Y-type subdwarf.

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arXiv2022

On the Nature of Ultracool White Dwarfs: Not so Cool Afterall

A recent analysis of the 100 pc white dwarf sample in the SDSS footprint demonstrated for the first time the existence of a well defined ultracool -- or IR-faint -- white dwarf sequence in the Hertzsprung-Russell diagram. Here we take advantage of this discovery to enlarge the IR-faint white dwarf sample threefold. We expand our selection to the entire Pan-STARRS survey footprint as well as the Montreal White Dwarf Database 100 pc sample, and identify 37 candidates with strong flux deficits in the optical. We present follow-up Gemini optical spectroscopy of 30 of these systems, and confirm all of them as IR-faint white dwarfs. We identify an additional set of 33 objects as candidates based on their colors and magnitudes. We present a detailed model atmosphere analysis of all 70 newly identified IR-faint white dwarfs together with 35 previously known objects reported in the literature. We discuss the physics of model atmospheres and show that the key physical ingredient missing in our previous generation of model atmospheres was the high-density correction to the He-minus free-free absorption coefficient. With new model atmospheres calculated for the purpose of this analysis, we now obtain significantly higher effective temperatures and larger stellar masses for these IR-faint white dwarfs than the Teff and M values reported in previous analyses, thus solving a two decade old problem. In particular, we identify in our sample a group of ultramassive white dwarfs in the Debye cooling phase with stellar parameters never measured before.

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arXiv2021

Gemini/GMOS Transmission Spectroscopy of the Grazing Planet Candidate WD 1856+534 b

WD 1856+534 b is a Jupiter-sized, cool giant planet candidate transiting the white dwarf WD 1856+534. Here, we report an optical transmission spectrum of WD 1856+534 b obtained from ten transits using the Gemini Multi-Object Spectrograph. This system is challenging to observe due to the faintness of the host star and the short transit duration. Nevertheless, our phase-folded white light curve reached a precision of 0.12 %. WD 1856+534 b provides a unique transit configuration compared to other known exoplanets: the planet is $8\times$ larger than its star and occults over half of the stellar disc during mid-transit. Consequently, many standard modeling assumptions do not hold. We introduce the concept of a `limb darkening corrected, time-averaged transmission spectrum' and propose that this is more suitable than $(R_{\mathrm{p}, λ} / R_{\mathrm{s}})^2$ for comparisons to atmospheric models for planets with grazing transits. We also present a modified radiative transfer prescription. Though the transmission spectrum shows no prominent absorption features, it is sufficiently precise to constrain the mass of WD 1856+534 b to be > 0.84 M$_\mathrm{J}$ (to $2 \, σ$ confidence), assuming a clear atmosphere and a Jovian composition. High-altitude cloud decks can allow lower masses. WD 1856+534 b could have formed either as a result of common envelope evolution or migration under the Kozai-Lidov mechanism. Further studies of WD 1856+534 b, alongside new dedicated searches for substellar objects around white dwarfs, will shed further light on the mysteries of post-main sequence planetary systems.

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arXiv2021

Infrared Excesses around Bright White Dwarfs from Gaia and unWISE. II

Infrared excesses around white dwarf stars indicate the presence of various astrophysical objects of interest, including companions and debris disks. In this second paper of a series, we present follow-up observations of infrared excess candidates from Gaia and unWISE discussed in the first paper, Paper I. We report space-based infrared photometry at 3.6 and 4.5 micron for 174 white dwarfs from the Spitzer Space Telescope and ground-based near-infrared J, H, and K photometry of 235 white dwarfs from Gemini Observatory with significant overlap between Spitzer and Gemini observations. This data is used to confirm or rule-out the observed unWISE infrared excess. From the unWISE-selected candidate sample, the most promising infrared excess sample comes from both colour and flux excess, which has a Spitzer confirmation rate of 95%. We also discuss a method to distinguish infrared excess caused by stellar or sub-stellar companions from potential dust disks. In total, we confirm the infrared excess around 62 white dwarfs, 10 of which are likely to be stellar companions. The remaining 52 bright white dwarf with infrared excess beyond two microns has the potential to double the known sample of white dwarfs with dusty exoplanetary debris disks. Follow-up high-resolution spectroscopic studies of a fraction of confirmed excess white dwarfs in this sample have discovered emission from gaseous dust disks. Additional investigations will be able to expand the parameter space from which dust disks around white dwarfs are found.

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arXiv2021

Measuring and Replicating the 1-20 um Energy Distributions of the Coldest Brown Dwarfs: Rotating, Turbulent and Non-Adiabatic Atmospheres

Cold, low-mass, field brown dwarfs are important for constraining the terminus of the stellar mass function, and also for optimizing atmospheric studies of exoplanets. In 2020 new model grids for such objects were made available: Sonora-Bobcat and ATMO 2020. Also, new candidate cold brown dwarfs were announced, and new spectroscopic observations at lambda ~4.8 um were published. In this paper we present new infrared photometry for some of the coldest brown dwarfs, and put the new data and models together to explore the properties of these objects. We reconfirm the importance of mixing in these atmospheres, which leads to CO and NH_3 abundances that differ by orders of magnitude from chemical equilibrium values. We also demonstrate that the new models retain the known factor >~3 discrepancy with observations at 2 <~ lambda um <~ 4, for brown dwarfs cooler than 600 K. We show that the entire 1 <~ lambda um <~ 20 energy distribution of six brown dwarfs with 260 <= T_eff K <= 475 can be well reproduced, for the first time, by model atmospheres which include dis-equilibrium chemistry as well as a photospheric temperature gradient which deviates from the standard radiative/convective equilibrium value. This change to the pressure-temperature profile is not unexpected for rotating and turbulent atmospheres which are subject to diabatic processes. A limited grid of modified-adiabat model colors is generated, and used to estimate temperatures and metallicities for the currently known Y dwarfs. A compilation of the photometric data used here is given in the Appendix.

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arXiv2020

Faint Standards for ZYJHK from the UKIDSS and VISTA Surveys

The currently defined "UKIRT Faint Standards" have JHK magnitudes between 10 and 15, with K_median=11.2. These stars will be too bright for the next generation of large telescopes. We have used multi-epoch observations taken as part of the UKIRT Infrared Deep Sky Survey (UKIDSS) and the Visible and Infrared Survey Telescope for Astronomy (VISTA) surveys to identify non-variable stars with JHK magnitudes in the range 16-19. The stars were selected from the UKIDSS Deep Extragalactic Survey (DXS) and Ultra Deep Survey (UDS), the WFCAM calibration data (WFCAMCAL08B), the VISTA Deep Extragalactic Observations (VIDEO) and UltraVISTA. Sources selected from the near-infrared databases were paired with the Pan-STARRS Data Release 2 of optical to near-infrared photometry and the Gaia astrometric Data Release 2. Colour indices and other measurements were used to exclude sources that did not appear to be simple single stars. From an initial selection of 169 sources, we present a final sample of 81 standard stars with ZYJHK magnitudes, or a subset, each with 20 to 600 observations in each filter. The new standards have Ks_median=17.5. The relative photometric uncertainty for the sample is <0.006 mag and the absolute uncertainty is estimated to be <~0.02 mag. The sources are distributed equatorially and are accessible from both hemispheres.

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arXiv2019

3.8um Imaging of 400-600K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB

Half of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 < lambda um < 5.5. We present new L' (3.43 < lambda um < 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L' from spectra for an additional two dwarfs. The targets include two binary systems which were imaged at a resolution of 0.25". One of these, WISEP J045853.90+643452.6AB, shows significant motion, and we present an astrometric analysis of the binary using Hubble Space Telescope, Keck Adaptive Optics, and Gemini images. We compare lambda ~4um observations to models, and find that the model fluxes are too low for brown dwarfs cooler than ~700K. The discrepancy increases with decreasing temperature, and is a factor of ~2 at T_eff=500K and ~4 at T_eff=400K. Warming the upper layers of a model atmosphere generates a spectrum closer to what is observed. The thermal structure of cool brown dwarf atmospheres above the radiative-convective boundary may not be adequately modelled using pure radiative equilibrium; instead heat may be introduced by thermochemical instabilities (previously suggested for the L- to T-type transition) or by breaking gravity waves (previously suggested for the solar system giant planets). One-dimensional models may not capture these atmospheres, which likely have both horizontal and vertical pressure/temperature variations.

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arXiv2018

Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample

This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station (NOFS) between 1989 and 2017, and the average uncertainty in the parallax values is 0.6 mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric dataset which spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for nineteen stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a sub-sample of 179 white dwarfs (WDs) at distances of 25 - 200 pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass and cooling age of each WD. Twenty-six WDs are newly classified and twelve systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of < 8 Gyr and masses close to the canonical 0.6 M_Sun.

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arXiv2017

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station (NOFS) are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here is new or updated $VI$ photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS $JHK_s$ near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Since large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.

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arXiv2017

The Y-Type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry and Near-Infrared Spectroscopy

The survey of the mid-infrared sky by the Wide-field Infrared Survey Explorer (WISE) led to the discovery of extremely cold low-mass brown dwarfs, classified as Y dwarfs, which extend the T class to lower temperatures. Twenty-four Y dwarfs are known at the time of writing. Here we present improved parallaxes for four of these, determined using Spitzer images. We give new photometry for four late-type T and three Y dwarfs, and new spectra of three Y dwarfs, obtained at Gemini Observatory. We also present previously unpublished photometry taken from HST, ESO, Spitzer and WISE archives of 11 late-type T and 9 Y dwarfs. The near-infrared data are put on to the same photometric system, forming a homogeneous data set for the coolest brown dwarfs. We compare recent models to our photometric and spectroscopic data set. We confirm that non-equilibrium atmospheric chemistry is important for these objects. Non-equilibrium cloud-free models reproduce well the near-infrared spectra and mid-infrared photometry for the warmer Y dwarfs with 425 <= T_eff K <= 450. A small amount of cloud cover may improve the model fits in the near-infrared for the Y dwarfs with 325 <= T_eff K <= 375. Neither cloudy nor cloud-free models reproduce the near-infrared photometry for the T_eff = 250 K Y dwarf W0855. We use the mid-infrared region, where most of the flux originates, to constrain our models of W0855. We find that W0855 likely has a mass of 1.5 - 8 Jupiter masses and an age of 0.3 - 6 Gyr. The Y dwarfs with measured parallaxes are within 20 pc of the Sun and have tangential velocities typical of the thin disk. The metallicities and ages we derive for the sample are generally solar-like. We estimate that the known Y dwarfs are 3 to 20 Jupiter-mass objects with ages of 0.6 to 8.5 Gyr.

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arXiv2017

Parallaxes and Infrared Photometry of three Y0 dwarfs

We have followed up the three Y0 dwarfs WISEPA J041022.71+150248.5, WISEPA J173835.53+273258.9 and WISEPC J205628.90+145953.3 using the UKIRT/WFCAM telescope/instruments. We find parallaxes that are more consistent and accurate than previously published values. We estimate absolute magnitudes in photometric pass-bands from $Y$ to $W3$ and find them to be consistent between the three Y0 dwarfs indicating the inherent cosmic absolute magnitude spread of these objects is small. We examine the MKO $J$ magnitudes over the four year time line and find small but significant monotonic variations. Finally we estimate physical parameters from a comparison of spectra and parallax to equilibrium and non-equilibrium models finding values consistent with solar metallicity, an effective temperature of 450-475\,K and log~g of 4.0-4.5.

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arXiv2016

Untangling the Near-IR Spectral Features in the Protoplanetary Environment of KH 15D

We report on Gemini/GNIRS observations of the binary T Tauri system V582 Mon (KH 15D) at three orbital phases. These spectra allow us to untangle five components of the system: the photosphere and magnetosphere of star B, the jet, scattering properties of the ring material, and excess near-IR radiation previously attributed to a possible self-luminous planet. We confirm an early-K subgiant classification for star B and show that the magnetospheric He I emission line is variable, possibly indicating increased mass accretion at certain times. As expected, the H$_2$ emission features associated with the inner part of the jet show no variation with orbital phase. We show that the reflectance spectrum for the scattered light has a distinctive blue slope and spectral features consistent with scattering and absorption by a mixture of water and methane ice grains in the 1-50 $μ$m size range. This suggests that the methane frost line is closer than $\sim$5 AU in this system, requiring that the grains be shielded from direct radiation. After correcting for features from the scattered light, jet, magnetosphere, and photosphere, we confirm the presence of leftover near-IR light from an additional source, detectable near minimum brightness. A spectral emission feature matching the model spectrum of a 10 M$_{J}$, 1 Myr old planet is found in the excess flux, but other expected features from this model are not seen. Our observations, therefore, tentatively support the picture that a luminous planet is present within the system, although they cannot yet be considered definitive.

astro-ph.EP↗