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Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs 1 , 2 . Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H 3 + and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported 3 . CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482 K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326 μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300 K centred at 1–10 mbar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H 3 + emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H 3 + at the higher pressure where the W1935 emission originates 4 . Methane emission from a very cool brown dwarf, perhaps arising from an aurora, has been detected in James Webb Space Telescope observations.

We obtained a series of four observations of the isolated neutron star Geminga over an 18 month period using the Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) on the Hubble Space Telescope in order to determine its trigonometric parallax. We find the parallax p=4.0c1.3mas, corresponding to a distance to Geminga of 250 sub(-62) super(+120) pc, a result 60% larger than the previously published value. The proper motion is 178.2c1.8mas/year. In this paper, we describe the analysis techniques in detail since the amplitude of the parallactic shift is smaller than the camera's pixel size. We fit each star in the images with an appropriate effective PSF and applied a distortion correction to generate stellar positions accurate to 0.01 pixels (0.5mas). The 134stars common to all images serve to establish a reference frame for alignment of the image series. Our observations were made around the times of maximum parallactic shift. We discuss the implications of this new distance measurement for the inferred radius of Geminga, and the neutron star equation of state.

In this case study, we describe the design and implementation of the Backyard Worlds: Cool Neighbors citizen science project, which combines image-level deep learning with Zooniverse-hosted online crowdsourcing to mine large astronomical sky maps for rare celestial objects called \"brown dwarfs.\" Specifically, Cool Neighbors uses machine learning to pre-select the sky images shown to volunteers. Cool Neighbors represents an excellent opportunity to interrogate the effects of incorporating artificial intelligence into a citizen science project; its sibling project, Backyard Worlds: Planet 9, uses no artificial intelligence, providing a natural point of comparison for participant engagement metrics. Through analysis of more than 10 million total Zooniverse classifications from the combination of Cool Neighbors and Backyard Worlds: Planet 9, among other results, we find (1) Cool Neighbors volunteers perform ~3x more classifications per unit of time invested than Backyard Worlds: Planet 9 volunteers, and (2) each registered Cool Neighbors participant performs ~2-5x more classifications than each registered Backyard Worlds: Planet 9 participant. We also discuss our measured approach to presenting the complementarity of machine learning and citizen science in volunteer-facing Cool Neighbors materials. Finally, we present a survey of advanced Backyard Worlds participants, which indicates that these citizen scientists are by and large not dissuaded from participating in Cool Neighbors because of its usage of artificial intelligence.

Young brown dwarfs and directly-imaged exoplanets have enticingly similar photometric and spectroscopic characteristics, indicating that their cool, low gravity atmospheres should be studied in concert. Similarities between the peculiar shaped H band, near and mid-IR photometry as well as location on color magnitude diagrams provide important clues about how to extract physical properties of planets from current brown dwarf observations. In this proceeding we discuss systems newly assigned to 10-150 Myr nearby moving groups, highlight the diversity of this uniform age-calibrated brown dwarf sample, and reflect on their implication for understanding current and future planetary data.

We have carried out an ALMA Cycle 2 survey of 15 confirmed or candidate low-mass (<0.2M⊙) members of the TW Hya Association (TWA) with the goal of detecting line emission from CO molecular gas and continuum emission from cold dust. Our targets have spectral types of M4-L0 and hence represent the extreme low end of the TWA's mass function. The survey has yielded a detection of 12CO(2–1) emission around TWA 34. This newly discovered ~10 Myr-old molecular gas disk lies just ~50pc from Earth.

We describe in this work the BASS survey for brown dwarfs in young moving groups of the solar neighborhood, and summarize the results that it generated. These include the discovery of the 2MASS J01033563–5515561 (AB)b and 2MASS J02192210–3925225 B young companions near the deuterium-burning limit as well as 44 new low-mass stars and 69 new brown dwarfs with a spectroscopically confirmed low gravity. Among those, ~20 have estimated masses within the planetary regime, one is a new L4 γ bona fide member of AB Doradus, three are TW Hydrae candidates with later spectral types (L1–L4) than all of its previously known members and six are among the first contenders for low-gravity ≥ L5 β/γ brown dwarfs, reminiscent of WISEP J004701.06+680352.1, PSO J318.5338–22.8603 and VHS J125601.92–125723.9 b. Finally, we describe a future version of this survey, BASS-Ultracool, that will specifically target ≥ L5 candidate members of young moving groups. First experimentations in designing the survey have already led to the discovery of a new T dwarf bona fide member of AB Doradus, as well as the serendipitous discoveries of an L9 subdwarf and an L5 + T5 brown dwarf binary.

ABSTRACT In our effort to complete the census of low-mass stars and brown dwarfs in the immediate solar neighborhood, we present spectra, photometry, proper motions, and distance estimates for 42 low-mass star and brown dwarf candidates discovered by the Wide-field Infrared Survey Explorer (WISE). We also present additional follow-up information on 12 candidates selected using WISE data but previously published elsewhere. The new discoveries include 15 M dwarfs, 17 L dwarfs, five T dwarfs, and five objects of other types. Among these discoveries is a newly identified \"unusually red L dwarf\" (WISE J223527.07 + 451140.9), four peculiar L dwarfs whose spectra are most readily explained as unresolved L + T binary systems, and a T9 dwarf (WISE J124309.61 + 844547.8). We also show that the recently discovered red L dwarf WISEP J004701.06 + 680352.1 may be a low-gravity object and hence young and potentially low-mass (< 25 MJup).

We report the discovery of the first brown dwarf binary system with a Y dwarf primary, WISE J033605.05\\(-\\)014350.4, observed with NIRCam on JWST with the F150W and F480M filters. We employed an empirical point spread function binary model to identify the companion, located at a projected separation of 84 milliarcseconds, position angle of 295 degrees, and with contrast of 2.8 and 1.8 magnitudes in F150W and F480M, respectively. At a distance of 10\\(\\,\\)pc based on its Spitzer parallax, and assuming a random inclination distribution, the physical separation is approximately 1\\(\\,\\)au. Evolutionary models predict for that an age of 1-5 Gyr, the companion mass is about 4-12.5 Jupiter masses around the 7.5-20 Jupiter mass primary, corresponding to a companion-to-host mass fraction of \\(q=0.61\\pm0.05\\). Under the assumption of a Keplerian orbit the period for this extreme binary is in the range of 5-9 years. The system joins a small but growing sample of ultracool dwarf binaries with effective temperatures of a few hundreds of Kelvin. Brown dwarf binaries lie at the nexus of importance for understanding the formation mechanisms of these elusive objects, as they allow us to investigate whether the companions formed as stars or as planets in a disk around the primary.

In our effort to complete the census of low-mass stars and brown dwarfs in the immediate solar neighborhood, we present spectra, photometry, proper motions, and distance estimates for 42 low-mass star and brown dwarf candidates discovered by the Wide-field Infrared Survey Explorer (WISE). We also present additional follow-up information on 12 candidates selected usingWISEdata but previously published elsewhere. The new discoveries include 15 M dwarfs, 17 L dwarfs, five T dwarfs, and five objects of other types. Among these discoveries is a newly identified “unusually red L dwarf” (WISE J223527.07 + 451140.9 J 223527.07 + 451140.9 ), four peculiar L dwarfs whose spectra are most readily explained as unresolvedL + T L + T binary systems, and a T9 dwarf (WISE J124309.61 + 844547.8 J 124309.61 + 844547.8 ). We also show that the recently discovered red L dwarfWISEP J004701.06 + 680352.1 J 004701.06 + 680352.1 may be a low-gravity object and hence young and potentially low-mass (< 25 M Jup < 25     M Jup ).

We present the results of a density-based clustering analysis of the 6-dimensional XYZ Galactic positions and UVW space velocities of nearby (\\(\\leq\\) 200 pc) Gaia EDR3 stars with radial velocities using HDBSCAN, in opposition to previous studies that only included positions and tangential velocities. Among the 241 recovered clusters, we identify more than 50 known associations, 32 new candidate stellar streams aged 100 Myr-3 Gyr, 9 extensions of known Theia groups uncovered by Kounkel & Covey (2019), and 8 newly recognized coronae around nearby open clusters. Three confirmed exoplanet-hosting stars and three more TESS transiting exoplanet candidates are part of the new groups discovered here, including TOI-1807 and TOI-2076 from Hedges et al. (2021) that were suspected to belong to a yet unidentified moving group. The new groups presented here were not previously recognized because of their older ages, low spatial density, and projection effects that spread out the tangential velocities of their nearby co-moving members. Several newly identified structures reach distances within 60 pc of the Sun, providing new grounds for the identification of isolated planetary-mass objects. The nearest member of the newly recognized corona of Volans-Carina is V419 Hya, a known young debris disk star at a distance of 22 pc. This study outlines the importance of further characterization of young associations in the immediate Solar neighborhood, which will provide new laboratories for the precise age calibration of nearby stars, exoplanets and substellar objects.