Daniella C. Bardalez Gagliuffi

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 (CW 2106), 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 (≈ −4.825 dex) of CW 2106, and obtain estimates of its mass ( M ≈ 50–62 M _Jup ), radius ( R ≈ 0.83–0.87 R _Jup ), effective temperature ( T _eff ≈ 1213 K), and surface gravity ( log g ≈ 5.28 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 CW 2106 to be composed primarily of enstatite (MgSiO ₃ ), removing ∼23% 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.

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 /Δ λ ≈ 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 945 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 ≈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 spectroscopic features of interest for future investigation. The SPIFF library presented here opens the door to efficient confirmation of candidate substellar objects and follow-up studies of population-level atmospheric properties of cold brown dwarfs.

We report the identification of a wide-separation comoving system consisting of the M dwarf L 378-6 and the L dwarf candidate CWISER J054003.47-401109.2, the latter discovered through the Backyard Worlds: Cool Neighbors project. Photometric distance estimates for the secondary are consistent with the Gaia parallax distance of the primary, and the two objects have very well-matched proper motions. We find an extremely low probability of chance alignment of 4 × 10 ⁻⁹ and a projected physical separation of 391 ± 2 au (angular separation of 13 . ″ 66 ± 0 . ″ 08 ). This pair represents a likely M dwarf-L dwarf benchmark system useful for testing brown dwarf evolutionary models. Follow-up spectroscopy and astrometry are required to further investigate and confirm the system’s properties.

The 14 Herculis (14 Her) 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.

The Backyard Worlds: Planet 9 citizen science project uses data from the Wide-field Infrared Survey Explorer to detect infrared objects with significant motion. In this work, we present the majority of the L and T dwarf candidates discovered through this effort. For each candidate, we provide proper motion measurements as well as optical, near-infrared, and mid-infrared photometry (when available), photometric spectral types and distance estimates. 3006 new motion-confirmed discoveries are presented in this work, 2357 with L-type photometric spectral types and 649 with T-type photometric spectral types. We also present an additional 80 objects as likely L or T dwarfs based on available photometry, but for which a significant motion measurement could not be obtained. We identify 28 objects in this sample as new comoving companions to higher-mass stars, and an additional nine sources that are candidate binary systems made up of two ultracool dwarfs of L type or later. Follow-up spectroscopic observations will be necessary to confirm spectral types and further characterize the sources discovered through this project. This work presents the largest single sample of motion-confirmed L and T dwarf discoveries to date, which would more than double the number of known L and T dwarfs, if confirmed. We wish to sincerely thank our citizen scientist collaborators for their monumental efforts that have directly impacted this project’s success.

We present a method for detecting faint, fast-moving objects in astronomical image time series using image segmentation via a recurrent convolutional neural network called SMDET. We use SMDET to segment Wide-field Infrared Survey Explorer (WISE) image time series that cover the full sky and rank sky regions according to the predicted presence of faint, fast objects. We visually inspect the sky regions ranked in the top 0.01% and discover hundreds of moving objects that are subjects of existing and forthcoming publications. We use a volume-limited (≤20 pc) sample of faint, high proper motion brown dwarfs to estimate ranking performance and find that we recover 94% of this sample in the top 0.01% ranked sky regions. We measure astrometry and photometry from the SMDET output and find that our search pushes fainter than any prior WISE-based search for high proper motion ( > 0 . ″ 35 yr - 1 ) objects. Our results demonstrate that our method effectively detects such objects in astronomical image time series and could be used to search existing datasets such as WISE single exposures and forthcoming datasets from facilities such as the Vera C. Rubin Observatory, Nancy Grace Roman Space Telescope, and Near‐Earth Object (NEO) Surveyor.

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 found 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 ≳85%, median component classification errors of ≲ 0.1 subtypes, and systematic classification uncertainties of ≲ 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.

We present the identification and characterization of 15 mid-to-late T dwarf candidates in the Euclid Quick Release 1 (Q1) data set, based on a combined photometric and spectroscopic analysis. Candidates were initially selected via color-based cuts in the Euclid Y _E − J _E and J _E − H _E color–color space, targeting the region occupied by ultracool dwarfs (UCDs) in synthetic photometry from the A. Sanghi et al. sample. From an initial pool of 38,845 sources, we extracted low-resolution near-infrared spectra from the Euclid Near-Infrared Spectrometer and Photometer instrument and applied a two-stage validation procedure that included spectral template fitting followed by visual inspection. Eight of the 15 validated candidates are newly identified objects with no prior literature association. We examined their morphological and photometric properties, and compared them with established spectral standards. Photometric distances were derived using band-averaged distance modulus estimates. We discuss the limitations and promise of the Euclid survey for UCD studies, and demonstrate the potential for discovering substellar populations beyond the reach of current wide-field surveys.

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 μ m) and MIRI F1000W, F1280W, and F1800W photometry for COCONUTS-2 b. In this work, we find a 99% probability of the system belonging to the Corona of Ursa Major moving group (414 ± 23 Myr) using BANYAN Σ and its full kinematics. We also reestimate the astrometry of COCONUTS-2b using the MIRI data. We support this membership with a comparison of the 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-2 b is a planetary-mass object (7.5 ± 0.4 M _Jup ), 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 M _Jup ). We identify absorption feature differences, which could indicate that 0825+2805 has stronger vertical mixing.