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Abstract 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 EuclidY_E − J_EandJ_E − H_Ecolor–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. 

ABSTRACT The Disc Detective project, a citizen science initiative, aims to identify circumstellar discs around stars by detecting objects with infrared (IR) excess using data from the Wide-field Infrared Survey Explorer (WISE). In this study, we investigate SIPS J2045–6332, a potential brown dwarf with significant IR excess in WISE and Two Micron All Sky Survey (2MASS) bands, initially identified by project volunteers. Despite early indicators of a circumstellar disc, discrepancies between observed brightness and expected spectral energy distribution (SED) models suggested unusual properties. To explore potential explanations, we created SED templates for spectral types M9 to L4 and compared them with SIPS J2045–6332’s photometric data, revealing an excess brightness that points to either an unresolved low-mass companion or a young, inflated primary star. Further analysis of IR spectral features and surface gravity indicators supports a youthful classification, estimating the object’s age at 26–200 million years. Observations also suggest the presence of a mid L-type companion at a projected distance of 6.7 au. This study highlights SIPS J2045–6332 as an intriguing system with unique IR characteristics and recommends follow-up observations with high-resolution telescopes to confirm the companion hypothesis and further characterize the system. 

Abstract We present an atmospheric retrieval analysis of a pair of highly variable, ∼200 Myr old, early T type planetary-mass exoplanet analogs SIMP J01365662+0933473 and 2MASS J21392676+0220226 using the Brewster retrieval framework. Our analysis, which makes use of archival 1–15μm spectra, finds almost identical atmospheres for both objects. For both targets, we find that the data is best described by a patchy, high-altitude forsterite (Mg₂SiO₄) cloud above a deeper, optically thick iron (Fe) cloud. Our model constrains the cloud properties well, including the cloud locations and cloud particle sizes. We find that the patchy forsterite slab cloud inferred from our retrieval may be responsible for the spectral behavior of the observed variability. Our retrieved cloud structure is consistent with the atmospheric structure previously inferred from spectroscopic variability measurements, but clarifies this picture significantly. We find consistent C/O ratios for both objects, which supports their formation within the same molecular cloud in the Carina-Near moving group. Finally, we note some differences in the constrained abundances of H₂O and CO, which may be caused by data quality and/or astrophysical processes such as auroral activity and their differing rotation rates. The results presented in this work provide a promising preview of the detail with which we will characterize extrasolar atmospheres with JWST, which will yield higher-quality spectra across a wider wavelength range. 

Abstract We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J−K)_MKOcolor of 2.97 ± 0.03 mag and aJ_MKO− W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH₄absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ–T0γ. We tentatively find that CWISE J0506+0738 is variable at 3–5μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in theβPic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object. 

Abstract While stars are often found in binary systems, brown dwarf binaries are much rarer. Brown dwarf–brown dwarf pairs are typically difficult to resolve because they often have very small separations. Using brown dwarfs discovered with data from the Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, we inspected other, higher-resolution, sky surveys for overlooked cold companions. During this process, we discovered the brown dwarf binary system CWISE J0146−0508AB, which we find has a very small chance alignment probability based on the similar proper motions of the components of the system. Using follow-up near-infrared spectroscopy with Keck/NIRES, we determined component spectral types of L4 and L8 (blue), making CWISE J0146−0508AB one of only a few benchmark systems with a blue L dwarf. At an estimated distance of ∼40 pc, CWISE J0146−0508AB has a projected separation of ∼129 au, making it the widest-separation brown dwarf pair found to date. We find that such a wide separation for a brown dwarf binary may imply formation in a low-density star-forming region.