arXiv subjects

Daniella C. Bardalez Gagliuffi

Publications and source records attributed to Daniella C. Bardalez Gagliuffi.

At least 19 recordsLinked to original sources

arXiv2026

Sinking Silicates I: Characterizing the benchmark system containing the T0 brown dwarf CWISE J210640.16+250729.0 using JWST

In this study, we present the full (97.3\% complete) 0.8--12.5 $μ$m spectral energy distribution (SED) of an L/T transition object, CWISE J210640.16+250729.0 (CW2106), using the James Webb Space Telescope (JWST). We provide a full characterization of the host star's elemental abundances and age. We empirically derive the bolometric luminosity ($L_{\rm bol}\approx-4.825$ $\textup{L}_\odot$) of CW2106, and obtain estimates of its mass (M$\approx50-62$ M$_{\rm Jup}$), radius (R$\approx0.83-0.87$ R$_{\rm Jup}$), effective temperature ($T_{\rm eff}$$\approx1213$ K), and surface gravity ($\log~g$$\approx5.28$ dex). We find the near-infrared (near-IR) spectrum ($0.8-2.5 ~μ$m) is best reproduced with cloudy atmospheric models while the mid-infrared (mid-IR) spectrum ($5-12.5 ~μ$m) is best reproduced with cloudless models. This suggests a cloud layer restricted to only the deepest observable parts of the atmosphere and is qualified by the lack of a 9 $μ$m silicate feature. Making use of the Mg/Si ratio of the primary, alongside thermochemical models, we predict the clouds in CW2106 to be composed primarily of enstatite (MgSiO$_3$), removing $\sim23\%$ of the bulk oxygen out of the atmosphere. Future retrieval studies will be able to help investigate the existence and full impact of these cloud species.

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arXiv2026

The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU

We present the first spectral analysis from the JWST Cycle 3 GO Program #6362, the Dyn-Atmo Survey of dynamical-atmospheric benchmarks, characterizing the atmospheres of directly-imaged companions with dynamical masses and measured orbits. This program has obtained moderate-resolution spectra (R$\sim$2700, 3-5$μ$m) using the NIRSpec/G395H IFU. We observe the T4-dwarf companion, HD 13724 B, companion to a G-type star at a projected angular separation of 0''2. Updated orbital monitoring constrains the mass to $38.3\pm0.6~M_{\rm{Jup}}$, which we use as a Gaussian prior when inferring the atmospheric state. We fit the continuum-subtracted spectrum using the BT-SETTL, Sonora Diamondback, Sonora Flame Skimmer, and NEWERA-PHOENIX self-consistent model grids, together with petitRADTRANS atmospheric retrievals. We adopt bulk parameter values of $T_\mathrm{eff}$=$1150\pm$195 K, $\log g$=5.1$\pm0.3$ dex, [M/H]=0.4$\pm$0.4, $\log_{10}(K_{zz})$=6.33$_{-2.22}^{+2.59}$, and C/O=$0.50\pm0.13$ using a bayesian average across model grids. We find degeneracies in the models between surface gravity, metallicity, and $K_{zz}$ for Sonora Diamondback and Flame Skimmer. The Flame Skimmer and NEWERA-PHOENIX vertical mixing strengths are incompatible, with Flame Skimmer finding a systematically lower value. The retrievals favor an atmosphere in chemical equilibrium, with enhanced metallicity and a solar C/O ratio, but with no detection of disequilibrium chemistry, and no detection of trace gases other than CH$_4$, CO$_{2}$, $^{12}$CO and H$_{2}$O. Ultimately, we identify critical challenges in forward modeling continuum-subtracted G395H spectra in the low signal-to-noise regime. We find that including independent dynamical mass measurements better constrains atmospheric parameters, but degeneracies between self-consistent model parameters limit accurate atmospheric parameter inferences.

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arXiv2026

Benchmark Brown Dwarfs as Chemical Laboratories: Linking System Bulk Properties to Atmospheric Retrievals

We present the first atmospheric retrieval analysis of two compositional benchmark mid-L dwarfs -- SDSSJ141659.78+500626.4 and GJ 499 C -- using the \textit{Brewster} retrieval framework, where the wide benchmark nature of these systems provides independent constraints on age and bulk composition from their stellar primaries. These targets were observed with JWST using NIRSpec Prism and MIRI LRS, providing low-resolution ($R$ $\sim$ 100) spectra between 0.6--14.0 $\mathrmμ$m with high signal-to-noise ratios (SNR $\sim$100 -- 600). For SDSSJ141659.78+500626.4, the retrieved cloud combination of a high-altitude enstatite slab and low-altitude iron deck clouds matches phase-equilibrium predictions based on the primary star's Mg/Si ratio. We retrieve a super-solar C/O = 0.71$^{+0.01}_{-0.01}$ and slightly metal-rich [M/H] = 0.22$^{+0.03}_{-0.03}$. This C/O ratio can only be reconciled with the value inferred for the primary if additional oxygen sequestration beyond the retrieved cloud mass is present, or if there are uncertainties in the adopted opacities or other model deficiencies. The inferred [C/H] and [O/H] are 0.31$\pm$0.03 and 0.19$\pm$0.03, respectively, which are consistent within the relatively large uncertainties of the host star abundances. For GJ 499 C, the retrieved silicon-monoxide and forsterite slab clouds are difficult to explain with simple phase-equilibrium assumptions, yielding Mg/Si $\sim$ 1.9. We estimate C/O = 0.69$^{+0.02}_{-0.02}$ and [M/H] = 0.13$^{+0.04}_{-0.06}$. For both objects, the inferred radii of 0.85$^{+0.01}_{-0.01}$ $R_{\mathrm{Jup}}$ and 1.00$^{+0.02}_{-0.02}$ $R_{\mathrm{Jup}}$ and masses of 73.7$^{+4.9}_{-9.2}$ $M_{\mathrm{Jup}}$ and 68.0$^{+8.5}_{-12.7}$ $M_{\mathrm{Jup}}$ are consistent with evolutionary models and system ages, highlighting the plausibility of our results.

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arXiv2026

The Architecture of the 14 Herculis System Suggests Primordial Ejection of a Massive Planet

The 14 Herculis system hosts two super-Jupiters on eccentric, significantly misaligned orbits. This orbital architecture represents a dynamical puzzle that demands explanation. In this work, we reproduce the system's dynamical history and current architecture using a large suite of N-body simulations of planet-planet scattering. Our results demonstrate that planet-planet scattering is able to reproduce 14 Her's peculiar orbital architecture, but only if additional massive bodies were initially present in the system that were subsequently ejected. The mass of any such ejected planet can in turn constrain the system's initial configuration. We also analyze the present-day secular evolution of the system and conclude that while there are most likely nontrivial eccentricity and inclination oscillations currently occurring, the magnitudes of these oscillations are not strong enough to allow tidal forces to meaningfully alter the system's architecture. Finally, we discuss how forthcoming observations from future Gaia data releases and the Roman mission may situate 14 Her's dynamical history within a broader, population-level framework.

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arXiv2026

A SPHEREx Pipeline and Spectral Library for Ultracool Dwarfs

We present a Python spectrophotometry extraction tool tailored for fast-moving point sources detected in the SPHEREx mission, and use it to construct a set of 0.75-5.0 $μ$m low-resolution ($λ/Δλ\sim 50$) spectrophotometry data products based on the SPHEREx Quick Release 2 (QR2) for a set of 6003 L0-Y1 ultracool dwarfs: 2050 known ultracool dwarfs, 3008 known photometric ultracool dwarf candidates, and 947 newly identified ultracool dwarfs. This work more than doubles the number of ultracool dwarfs with spectroscopy, from 3449 to 7402. We provide SPHEREx templates for each spectral subtype and a set of tools to assign automated spectral types. The QR2 data release generates spectrophotometry with an average signal-to-noise per spectral channel above $\sim$10 for most objects with WISE W2 magnitudes of 14.0 mag and brighter. The compiled data set is made available publicly at https://mocadb.ca, where new spectral compilations from future data releases will also be made available as they are published. These new data provide a significant increase in the number of substellar objects for which the 2.4-5.0 $μ$m window is now accessible, making it possible to probe important molecular chemistry of key CNOS-bearing species for the coolest brown dwarfs. We flag 2668 ultracool dwarfs as candidate young brown dwarfs, 250 as candidate subdwarfs, and 865 as possibly otherwise peculiar for future investigation. The SPIFF library presented here opens the doors to efficient confirmation of candidate substellar objects and follow-up studies of population-level atmospheric properties of cold brown dwarfs.

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arXiv2026

The Y Dwarf Population with HST: unlocking the secrets of our coolest neighbours -- III. Near-Infrared Photometry

Y dwarfs represent the coldest class of brown dwarfs, with effective temperatures below 500K, and provide unique analogues to cold giant exoplanets. We present a large compilation of uniform near-infrared photometry from the Hubble Space Telescope for 21 Y dwarfs across multiple WFC3/IR filters, including the F105W, F125W and F160W bands. We employed refined PSF-fitting and calibration procedures to reach photometric uncertainties at the 0.02-0.05 mag level for most targets. Combined with precise parallax measurements, our data reveal well-defined Y-dwarf sequences in near-infrared colour-magnitude diagrams, observed with a markedly improved tightness. Known photometric trends emerge with minimal scatter, including the continuous redward progression in F125W-F160W with decreasing temperature, and the blueward trend in F105W-F125W with possible hints of a reversal around 350K. Comparisons to the ATMO, Sonora Elf Owl, and Lacy & Burrows atmospheric models highlight systematic discrepancies, in particular F105W-F125W and F105W-F160W colours predicted to be too red. Low-metallicity grids provide the best fits to the global Y-dwarf population, although closer inspection across wavelengths shows that these preferences likely reflect compensating effects in missing or incomplete physics rather than true population-level abundances. While some atmospheric diversity is expected among Y dwarfs, their tight observational sequences and systematic offsets from model predictions reveal that key physical and chemical processes remain inadequately captured in current grids. Our results underscore the importance of high-precision, internally consistent datasets in robustly tracing the Y-dwarf cooling sequence and providing the empirical constraints needed to advance theoretical models at the lowest temperatures.

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arXiv2025

Identifying and Characterizing Very Low Mass Spectral Blend Binaries with Machine Learning Methods

We present an approach to identifying and characterizing unresolved, very low mass spectral blend binaries composed of late-M, L, and T dwarfs using machine learning methodologies. We generated and evaluated a series of hierarchical random forest models to distinguish spectral blends from single very low-mass dwarfs, and to classify their primary and secondary components. Models were trained on a sample of single and synthesized binary templates generated from empirical spectra. We explored various aspects of the design of our models, and find that models trained on a full range of single and binary combinations have the best performance for identification and component classification. These models achieve binary identification recall and precision of $\gtrsim$85%, median component classification errors of $\lesssim$0.1 subtypes, and systematic classification uncertainties of $\lesssim$1 subtype, outperforming index-based methods in terms of fidelity, range, and speed. Optimal performance is achieved for binaries composed of L and T dwarf primaries and late-L and T dwarf secondaries. When applied to the spectra of previously confirmed very low-mass binaries, model performance is degraded due to the prevalence of systems with similar component types, but remains high in the optimal performance range. We propose potential improvements to these models, which can be used to explore binary populations among the thousands to millions of very low-mass stars and brown dwarfs anticipated with large-scale spectral surveys such as SPHEREx and Euclid.

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arXiv2025

The Diversity of Cold Worlds: Age and Characterization of the Exoplanet COCONUTS-2b

Studying cold brown dwarfs is key to understanding the diverse characteristics of cold giant exoplanets atmospheres. COCONUTS-2, is a wide binary system composed of a T9 brown dwarf and an M3 star, which presents a unique opportunity to characterize a cold benchmark brown dwarf. As part of a JWST program to study the range of physical and atmospheric properties of the coldest brown dwarfs, we obtained NIRSpec G395H spectra (R~2700, 2.87-5.13 um) and MIRI F1000W, F1280W, and F1800W photometry for COCONUTS-2b. In this work, we find a 99% probability of the system belonging to the Corona of Ursa Major (414+/-23 Myr) using BANYAN Sigma and its full kinematics. We also re-estimate the astrometry of COCONUTS-2b using the MIRI data. We support the membership with a comparison of rotation period, metallicity and C/O ratio of the group with those of the COCONUTS-2 system. We also calculate its bolometric luminosity, which combined with our age estimation, allows us to derive its mass, effective temperature, surface gravity, and radius with high precision. As a result of our analysis, we support the conclusion that COCONUTS-2b is a planetary mass object (7.5+/-0.4 MJup) which was likely formed via the same mechanism as stars. In addition we compare the JWST spectrum to another object in the sample, J082507.35+280548.5 (0825+2805), a Y0.5 brown dwarf, which is a candidate member of the same moving group, but has a lower mass (3.7+/-0.2 MJup). We identify absorption feature differences which could indicate that 0825+2805 has stronger vertical mixing.

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arXiv2025

Diversity of Cold Worlds: Predicted Near- to Mid-infrared Spectral Signatures of a Cold Brown Dwarf with Potential Auroral Heating

Recent JWST/NIRSpec observations have revealed strong methane emission at 3.326 microns in the $\approx$482 K brown dwarf CWISEP J193518.59$-$154620.3 (W1935). Atmospheric modeling suggests the presence of a $\approx$300 K thermal inversion in its upper atmosphere, potentially driven by auroral activity. We present an extension of the retrieved spectra of W1935 with and without inversion spanning 1--20 microns, to identify thermal inversion-sensitive spectral features and explore the origin of the object's peculiar characteristics. Our analysis indicates that atmospheric heating contributes approximately 15% to the bolometric luminosity. The model with inversion predicts an additional similar-strength methane emission feature at 7.7 microns and tentative ammonia emission features in the mid-infrared. Wavelengths beyond $\sim$2 microns are significantly influenced by the inversion, except for the 4.1--5.0 microns CO$_2$ and CO features that originate from atmospheric layers deeper than the region where the inversion occurs. W1935 appears as an outlier in Spitzer/IRAC mid-infrared color-magnitude diagrams (CMDs) based on the $m_{\rm Ch1}-m_{\rm Ch2}$ (IRAC 3.6 microns $-$ 4.5 microns) color, but exhibits average behavior in all other combinations that trace clear sequences. This anomaly is likely due to the Ch2 filter probing vertical mixing-sensitive CO$_2$ and CO features that do not correlate with temperature or spectral type. We find that the thermal inversion tends to produce bluer $m_{\rm Ch1}-m_{\rm Ch2}$ colors, so the overluminous and/or redder position of W1935 in diagrams involving this color cannot be explained by the thermal inversion. This analysis provides insights into the intriguing dispersion of cold brown dwarfs in mid-infrared CMDs and sheds light on their spectral diversity.

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arXiv2025

Discovery of the Second Y+Y Dwarf Binary System: CWISEP J193518.59-154620.3

We present the discovery of a companion to the Y-dwarf, CWISEP J193518.59-154620.3, the second Y-Y dwarf binary detected to date. Y-dwarfs are the coldest known free-floating objects ($<$ 500 K) and on average represent the lowest mass objects directly formed through turbulent fragmentation of a molecular cloud. Studying their multiplicity allows us to place strong constraints on the ability to form multiple systems of planetary masses and approaching the opacity limit of fragmentation. Due to their physical properties, Y-dwarfs also serve as analogs to gas giant planets. CWISEP J193518.59-154620.3 has been shown to have a unique methane emission feature in its near infrared spectrum at 3.326 $μ$m, potentially indicative of auroral processes without a clear origin. CWISEP J193518.59-154620.3 was observed with JWST's MIRI in the F1000W, F1280W, and F1800W filters. We applied a point-spread function (PSF) fitting algorithm using empirically derived PSF models and resolve a companion in the F1000W and F1280W filters separated by 172 milli-arcseconds, 2.48 au assuming the distance of 14.43 pc. Using the ATMO2020 evolutionary models, we estimate a mass of 12-39 $M_{\rm Jup}$ for the primary and 7-24 $M_{\rm Jup}$ for the companion assuming an age of 1-10 Gyr for a mass ratio of 0.55-0.62, resulting in an estimated period of 16-28 years. It is unknown which component of this binary exhibits the methane emission feature. We also resolve known companions WISE J014656.66+423410.0B and WISE J171104.60+350036.8B using MIRI data and present their F1000W and F1280W photometry.

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arXiv2025

JWST Coronagraphic Images of 14 Her c: a Cold Giant Planet in a Dynamically Hot, Multi-planet System

Most observed multi-planet systems are coplanar, in a dynamically "cold" configuration of concentric orbits like our own Solar System. With the James Webb Space Telescope (JWST) we have detected 14 Her c, the first mature and cold exoplanet directly imaged in a dynamically "hot", multi-planet system. With large eccentricities and a nonzero mutual inclination, the present-day architecture of this system points to a turbulent past and ongoing angular momentum exchange between the planetary orbits of 14 Her b and c. The temperature of 14 Her c rivals both the coldest imaged exoplanet and the coldest known brown dwarf. Moreover, its photometry at 4.4 mu is consistent with the presence of carbon disequilibrium chemistry and water ice clouds in its atmosphere. 14 Her c presents a unique laboratory to study giant planet formation, dynamical evolution of multi-planet system architectures, and atmospheric composition and dynamics in extremely cold worlds.

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arXiv2025

Diversity of Cold Worlds: A Near Complete Spectral Energy Distribution for 2MASS J04151954-0935066 using JWST

We present the a near complete spectral energy distribution (SED) for an extrasolar world: the T8 brown dwarf 2MASS~J04151954$-$0935066. Spanning from optical to mid-infrared (0.7--20.4 micron) wavelengths, the SED for this substellar atmosphere is constructed from new JWST NIRSpec G395H ($R\sim$2700) and Magellan FIRE echelle ($R\sim$8000) near-infrared spectra, along with MIRI mid-infrared photometry complemented by spectra from Keck I, IRTF, Magellan, AKARI, Spitzer and photometry from various surveys and missions. The NIRSpec G395H spectrum reveals strong molecular absorptions from NH$_{3}$, CH$_{4}$, H$_{2}$S, CO$_{2}$ and H$_{2}$O at approximately 3.00, 3.35, 3.95, 4.25, and 5.00 micron respectively, along with the presence of a CO absorption feature detected mainly at $\sim$ 4.6 micron. We detect no absorption of near-infrared K I doublets in the $R\sim8000$ FIRE spectra. In the mid-infrared IRS spectrum, we tentatively identify a new CO$_{2}$ feature at 14--16 micron. The comprehensive SED allows us to empirically constrain bolometric luminosity, effective temperature, mass and radius. Additionally, we demonstrate that the NIRSpec G395H resolution, the highest allowable by JWST, enables a precise radial velocity measurement of $47.1\pm1.8$ km s$^{-1}$ for the object, in agreement with previous measurements.

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arXiv2025

The Diversity of Cold Worlds: a blended-light binary straddling the T/Y transition in brown dwarfs

We present the first brown dwarf spectral binary characterized with JWST: WISE J014656.66+423410.0, the coldest blended-light brown dwarf binary straddling the T/Y transition. We obtained a moderate resolution (R$\sim$2700) G395H spectrum of this unresolved binary with JWST/NIRSpec and we fit it to late-T and Y dwarf spectra from JWST/NIRSpec, and model spectra of comparable temperatures, both as individual spectra and pairs mimicking an unresolved binary system. We find that this tightly-separated binary is likely composed of two unequal-brightness sources with a magnitude difference of $0.50\pm0.08$ mag in IRAC [4.5] and a secondary $1.01\pm0.13$ mag redder than the primary in [3.6]-[4.5]. Despite the large color difference between the best fit primary and secondary, their temperature difference is only $92\pm23$\,K, a feature reminiscing of the L/T transition. Carbon disequilibrium chemistry strongly shapes the mid-infrared spectra of these sources, as a complex function of metallicity and surface gravity. While a larger library of JWST/NIRSpec spectra is needed to conclusively examine the peculiarities of blended-light sources, this spectral binary is a crucial pathfinder to both understand the spectral features of planetary-mass atmospheres and detect binarity in unresolved, moderate-resolution spectra of the coldest brown dwarfs.

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arXiv2025

JWST 1.5 μm and 4.8 μm Photometry of Y Dwarfs

Brown dwarfs lack nuclear fusion and cool with time; the coldest known have an effective temperature below 500 K, and are known as Y dwarfs. We present a James Webb Space Telescope (JWST) photometric dataset of Y dwarfs: twenty-three were imaged in wide-field mode, 20 using NIRCam with the F150W and F480M filters, and 3 using NIRISS with the F480M filter. We present an F480M vs. F150W $-$ F480M color-magnitude diagram for our sample, and other brown dwarfs with F150W and F480M colors synthesized from JWST spectra by Beiler et al. (2024). For one target, WISEA J083011.95$+$283716.0, its detection in the near-infrared confirms it as one of the reddest Y dwarfs known, with F150W $-$ F480M $= 9.62$ mag. We provide its updated parallax and proper motion. One of the Beiler et al. Y dwarfs, CWISEP J104756.81+545741.6, is unusually blue, consistent with strong CO absorption seen in its spectrum which the F480M filter is particularly sensitive to. The strong CO and the kinematics of the object suggest it may be very low-mass and young. We update the resolved photometry for the close binary system WISE J033605.05$-$014350.4 AB, and find that the secondary is almost as cold as WISE 085510.83$-$071442.5, with $T_{\rm eff} \lesssim 300$ K, however the F150W $-$ F480M color is significantly bluer, possibly suggesting the presence of water clouds. Astrometry is measured at the JWST epoch for the sample which is consistent with parallax and proper motion values reported by Kirkpatrick et al. (2021) and Marocco et al. (in prep).

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arXiv2025

The Y Dwarf Population with HST: unlocking the secrets of our coolest neighbours -- II. Parallaxes and Proper Motions

We present astrometric results from a Hubble Space Telescope (HST) campaign aimed at determining precise distances for cold Y-type brown dwarfs. Combining observations from a dedicated HST/WFC3 program with archival data, we derive astrometric solutions for 15 nearby Y dwarfs, by linking the high-precision relative astrometry from Hubble to the high-accuracy Gaia DR3 absolute reference system, using stars present in both to anchor the two frames of reference. We reach uncertainties on parallaxes below the 1-mas level for half of the sample, and down to 3 mas for two thirds of the targets, or relative precisions <1% in most cases and 2-5x improvements over previous measurements. For the remaining targets, we achieved slightly lower precisions on parallaxes (5-12 mas, 5-10%), correlated with the lower signal-to-noise of the faintest targets. The precision reached in our derived proper motions is around 0.1-0.4 mas/yr for most targets, and up to 1-2 mas/yr for less precise cases. Our estimated parallaxes and proper motions are generally in good agreement with literature values, and consistent to 1-2 sigma with recent Spitzer-derived parallaxes in most cases. These new astrometric solutions provide important validation of these objects' distances and sky motions, especially given the large disparities seen in previous estimates. Our results demonstrate the power of HST combined with Gaia to measure highly-precise absolute astrometry for faint brown dwarfs, and highlights the limitations reached for the reddest and coldest objects, for which JWST will certainly provide a favourable platform to improve these results.

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arXiv2024

JWST/NIRCam 4-5 $μ$m Imaging of the Giant Planet AF Lep b

With a dynamical mass of $3 \, M_\mathrm{Jup}$, the recently discovered giant planet AF Lep b is the lowest-mass imaged planet with a direct mass measurement. Its youth and spectral type near the L/T transition make it a promising target to study the impact of clouds and atmospheric chemistry at low surface gravities. In this work, we present JWST/NIRCam imaging of AF Lep b. Across two epochs, we detect AF Lep b in F444W ($4.4 \, \mathrm{μm}$) with S/N ratios of $9.6$ and $8.7$, respectively. At the planet's separation of $320 \, \mathrm{mas}$ during the observations, the coronagraphic throughput is ${\approx}7\%$, demonstrating that NIRCam's excellent sensitivity persists down to small separations. The F444W photometry of AF Lep b affirms the presence of disequilibrium carbon chemistry and enhanced atmospheric metallicity. These observations also place deep limits on wider-separation planets in the system, ruling out $1.1 \, M_\mathrm{Jup}$ planets beyond $15.6 \, \mathrm{au}$ ($0.58$ arcsec), $1.1 \, M_\mathrm{Sat}$ planets beyond $27 \, \mathrm{au}$ ($1$ arcsec), and $2.8 \, M_\mathrm{Nep}$ planets beyond $67 \, \mathrm{au}$ ($2.5$ arcsec). We also present new Keck/NIRC2 $L'$ imaging of AF Lep b; combining this with the two epochs of F444W photometry and previous Keck $L'$ photometry provides limits on the long-term $3{-}5 \, \mathrm{μm}$ variability of AF Lep b on months-to-years timescales. AF Lep b is the closest-separation planet imaged with JWST to date, demonstrating that planets can be recovered well inside the nominal (50\% throughput) NIRCam coronagraph inner working angle.

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arXiv2024

Simulating Brown Dwarf Observations for Various Mass Functions, Birthrates, and Low-mass Cutoffs

After decades of brown dwarf discovery and follow-up, we can now infer the functional form of the mass distribution within 20 parsecs, which serves as a constraint on star formation theory at the lowest masses. Unlike objects on the main sequence that have a clear luminosity-to-mass correlation, brown dwarfs lack a correlation between an observable parameter (luminosity, spectral type, or color) and mass. A measurement of the brown dwarf mass function must therefore be procured through proxy measurements and theoretical models. We utilize various assumed forms of the mass function, together with a variety of birthrate functions, low-mass cutoffs, and theoretical evolutionary models, to build predicted forms of the effective temperature distribution. We then determine the best fit of the observed effective temperature distribution to these predictions, which in turn reveals the most likely mass function. We find that a simple power law ($dN/dM \propto M^{-α}$) with $α\approx 0.5$ is optimal. Additionally, we conclude that the low-mass cutoff for star formation is $\lesssim0.005M_{\odot}$. We corroborate the findings of Burgasser (2004) which state that the birthrate has a far lesser impact than the mass function on the form of the temperature distribution, but we note that our alternate birthrates tend to favor slightly smaller values of $α$ than the constant birthrate. Our code for simulating these distributions is publicly available. As another use case for this code, we present findings on the width and location of the subdwarf temperature gap by simulating distributions of very old (8-10 Gyr) brown dwarfs.

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arXiv2024

An Informed and Systematic Method to Identify Variable mid-L dwarfs

Most brown dwarfs show some level of photometric or spectral variability. However, finding the most variable dwarfs more suited for a thorough variability monitoring campaign remained a challenge until a few years ago with the design of spectral indices to find the most likely L and T dwarfs using their near-infrared single-epoch spectrum. In this work, we designed and tested near-infrared spectral indices to pre-select the most likely variable L4-L8 dwarfs, complementing the indices presented by Ashraf et al. (2022) and Oliveros-Gomez et al. (2022). We used time-resolved near-infrared Hubble Space Telescope Wide Field Camera 3 spectra of an L6.0 dwarf, LP 261-75b, to design our novel spectral indices. We tested these spectral indices on 75 L4.0-L8.0 near-infrared SpeX/IRTF spectra, providing 27 new variable candidates. Our indices have a recovery rate of 80 percent and a false negative rate of 25 percent. All the known non-variable brown dwarfs were found to be non-variable by our indices. We estimated the variability fraction of our sample to be near 51 percent, which agrees with the variability fractions provided by Buenzli et al. (2014), Radigan et al. (2014), and Metchev et al. (2015) for L4-L8 dwarfs. These spectral indices may support in the future, the selection of the most likely variable directly-imaged exoplanets for studies with the James Webb Space Telescope and as well as the 30-m telescopes.

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