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Zonal (latitudinal) winds dominate the bulk flow of planetary atmospheres. For gas giant planets such as Jupiter, the motion of clouds can be compared with radio emissions from the magnetosphere, which is connected to the planet’s interior, to determine the wind speed. In principle, this technique can be applied to brown dwarfs and/or directly imaged exoplanets if periods can be determined for both the infrared and radio emissions. We apply this method to measure the wind speeds on the brown dwarf 2MASS J10475385+2124234. The difference between the radio period of 1.751 to 1.765 hours and infrared period of 1.741 ± 0.007 hours implies a strong wind (+650 ± 310 meters per second) proceeding eastward. This could be due to atmospheric jet streams and/or low frictional drag at the bottom of the atmosphere.

We present a uniform forward-modeling analysis of 90 late-M and L dwarfs in nearby young (∼10–200 Myr) moving groups, the Pleiades, and the Hyades using low-resolution (R ≈ 150) near-infrared (0.9–2.4 μm) spectra and the BT-Settl model atmospheres. We derive the objects’ effective temperatures, surface gravities, radii, and masses by comparing our spectra to the models using a Bayesian framework with nested sampling and calculate the same parameters using evolutionary models. Assuming the evolutionary-based parameters are more robust, our spectroscopically inferred parameters from BT-Settl exhibit two types of systematic behavior for objects near the M-L spectral type boundary. Several objects are clustered around T eff ≈ 1800 K and logg≈5.5 dex, implying impossibly large masses (150–1400 M Jup), while others are clustered around T eff ≳ 3000 K and logg≲3.0 dex, implying unphysically low masses and unreasonably young ages. We find the fitted BT-Settl model spectra tend to overpredict the peak J- and H-band flux for objects located near the M-L boundary, suggesting the dust content included in the model atmospheres is insufficient to match the observations. By adding an interstellar medium–like reddening law to the BT-Settl model spectra, we find the fits between models and observed spectra are greatly improved, with the largest reddening coefficients occurring at the M-L transition. This work delivers a systematic examination of the BT-Settl model atmospheres and constitutes the largest spectral analysis of benchmark late-M- and L-type brown dwarfs to date.

Low-mass stars and substellar objects are essential in tracing the initial mass function (IMF). We study the nearby young σ Orionis cluster (d ∼ 408 pc, age ∼ 1.8 Myr) using deep near-infrared (NIR) photometric data in the J, W, and H bands from WIRCam on the Canada–France–Hawaii Telescope. We use the water absorption feature to select brown dwarfs photometrically and confirm their nature spectroscopically with IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and those of literature sources using astrometry from Gaia DR3. We obtain NIR spectra for 28 very-low-mass stars and brown dwarfs and estimate their spectral type between M3 and M8.5 (masses ranging between 0.3 and 0.01 M ⊙). Apart from these, we also identify five new planetary-mass candidates which require further spectroscopic confirmation of youth. We compile a comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of ∼19–0.004 M ☉. We estimate the star-to-brown-dwarf ratio to be ∼4, within the range reported for other nearby star-forming regions. With the updated catalog of members we trace the IMF down to 4 M Jup and we find that a two-segment power law fits the substellar IMF better than a log-normal distribution.

The coldest Y spectral type brown dwarfs are similar in mass and temperature to cool and warm (∼200–400 K) giant exoplanets. We can therefore use their atmospheres as proxies for planetary atmospheres, testing our understanding of physics and chemistry for these complex, cool worlds. At these cold temperatures, their atmospheres are cold enough for water clouds to form, and chemical timescales increase, increasing the likelihood of disequilibrium chemistry compared to warmer classes of planets. JWST observations are revolutionizing the characterization of these worlds with high signal-to-noise, moderate-resolution near- and mid-infrared spectra. The spectra have been used to measure the abundances of prominent species, like water, methane, and ammonia; species that trace chemical reactions, like carbon monoxide; and even isotopologues of carbon monoxide and ammonia. Here, we present atmospheric retrieval results using both published fixed-slit (Guaranteed Time Observation program 1230) and new averaged time series observations (GO program 2327) of the coldest known Y dwarf, WISE 0855–0714 (using NIRSpec G395M spectra), which has an effective temperature of ∼264 K. We present a detection of deuterium in an atmosphere outside of the solar system via a relative measurement of deuterated methane (CH3D) and standard methane. From this, we infer the D/H ratio of a substellar object outside the solar system for the first time. We also present a well-constrained part-per-billion abundance of phosphine (PH3). We discuss our interpretation of these results and the implications for brown dwarf and giant exoplanet formation and evolution.

We present the characterization of the low-gravity M6 dwarf 2MASS J06195260-2903592, previously identified as an unusual field object based on its strong IR excess and variable near-IR spectrum. Multiple epochs of low-resolution (R ≈ 150) near-IR spectra show large-amplitude (≈0.1–0.5 mag) continuum variations on timescales of days to 12 yr, unlike the small-amplitude variability typical for field ultracool dwarfs. The variations between epochs are well-modeled as changes in the relative extinction (ΔA V ≈ 2 mag). Similarly, Panoramic Survey Telescope and Rapid Response System 1 optical photometry varies on timescales as long as 11 yr (and possibly as short as an hour) and implies comparable A V changes. Near Earth Object Wide-field Infrared Survey Explorer mid-IR light curves also suggest changes on 6 month timescales, with amplitudes consistent with the optical/near-IR extinction variations. However, near-IR spectra, near-IR photometry, and optical photometry obtained in the past year indicate that the source can also be stable on hourly and monthly timescales. From comparison to objects of similar spectral type, the total extinction of 2MASS J0619-2903 seems to be A V ≈ 4–6 mag, with perhaps epochs of lower extinction. Gaia Early Data Release 3 (EDR3) finds that 2MASS J0619-2903 has a wide-separation (1.′2 = 10,450 au) stellar companion, with an isochronal age of 31−10+22 Myr and a mass of 0.30−0.03+0.04 M ☉. Adopting this companion’s age and EDR3 distance (145.2 ± 0.6 pc), we estimate a mass of 0.11–0.17 M ☉ for 2MASS J0619-2903. Altogether, 2MASS J0619-2903 appears to possess an unusually long-lived primordial circumstellar disk, perhaps making it a more obscured analog to the “Peter Pan” disks found around a few M dwarfs in nearby young moving groups.

Nearly 500 brown dwarfs have been discovered in recent years. The majority of these brown dwarfs exist in the solar neighborhood, yet determining their fundamental properties (mass, age, temperature & metallicity) has proved to be quite difficult, with current estimates relying heavily on theoretical models. Binary brown dwarfs provide a unique opportunity to empirically determine fundamental properties, which can then be used to test model predictions. In addition, the observed binary fractions, separations, mass ratios, & orbital eccentricities can provide insight into the formation mechanism of these low-mass objects. I will review the results of various brown dwarf multiplicity studies, and will discuss what we have learned about the formation and evolution of brown dwarfs by examining their binary properties as a function of age and mass.

In recent years, all-sky surveys have uncovered a new and interesting population of young (≈10–200 Myr), nearby substellar objects. Many of these objects have inferred masses and temperatures that overlap those of directly imaged exoplanets. These young brown dwarfs provide valuable analogs to young, dusty exoplanets in a context where detailed spectroscopic observations across a broad range of wavelengths and at high S/N are possible. How do the temperatures inferred by atmospheric models and evolutionary models compare? Can we determine the formation mechanism of a young planetary-mass object? How well do we understand the role that disequilibrium chemistry and dust clouds play in the atmospheres of these objects? We review the successes and challenges in determining the fundamental properties (mass, log(g), effective temperature) of young substellar objects, both brown dwarfs and gas-giant exoplanets.

We report the identification of 89 new systems containing ultracool dwarf companions to main-sequence stars and white dwarfs, using the citizen science project Backyard Worlds: Planet 9 and cross-reference between Gaia and CatWISE2020. 32 of these companions and 33 host stars were followed up with spectroscopic observations, with companion spectral types ranging from M7–T9 and host spectral types ranging from G2–M9. These systems exhibit diverse characteristics, from young to old ages, blue to very red spectral morphologies, potential membership to known young moving groups, and evidence of spectral binarity in nine companions. 20 of the host stars in our sample show evidence for higher-order multiplicity, with an additional 11 host stars being resolved binaries themselves. We compare this sample’s characteristics with those of the known stellar binary and exoplanet populations, and find our sample begins to fill in the gap between directly imaged exoplanets and stellar binaries on mass ratio–binding energy plots. With this study, we increase the population of ultracool dwarf companions to FGK stars by ∼42%, and more than triple the known population of ultracool dwarf companions with separations larger than 1000 au, providing excellent targets for future atmospheric retrievals.

We report the discovery of substellar objects in the young star cluster IC 348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the Perseus star-forming complex. The substellar candidates are selected using narrowband imaging, i.e., on and off photometric technique with a filter centered around the water absorption feature at 1.45 μm, a technique proven to be efficient in detecting water-bearing substellar objects. Our spectroscopic observations confirm three brown dwarfs in IC 348. In addition, the source WBIS 03492858+3258064, reported in this work, is the first confirmed brown dwarf discovered toward Barnard 5. Together with the young stellar population selected via near- and mid-infrared colors using the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer, we diagnose the relation between stellar versus substellar objects with the associated molecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud members across the Perseus region, we propose the star formation scenario of the complex under influence of the nearby OB association.

A complete accounting of nearby objects—from the highest-mass white dwarf progenitors down to low-mass brown dwarfs—is now possible, thanks to an almost complete set of trigonometric parallax determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census of objects within a Sun-centered sphere of 20 pc radius and check published literature to decompose each binary or higher-order system into its separate components. The result is a volume-limited census of ∼3600 individual star formation products useful in measuring the initial mass function across the stellar (<8M ⊙) and substellar (≳5M Jup) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8M ⊙ and a divergence at lower masses. Our 20 pc space densities are best fit with a quadripartite power law, ξ(M)=dN/dM∝M−α , with long-established values of α = 2.3 at high masses (0.55 < M < 8.00M ⊙), and α = 1.3 at intermediate masses (0.22 < M < 0.55M ⊙), but at lower masses, we find α = 0.25 for 0.05 < M < 0.22M ⊙, and α = 0.6 for 0.01 < M < 0.05M ⊙. This implies that the rate of production as a function of decreasing mass diminishes in the low-mass star/high-mass brown dwarf regime before increasing again in the low-mass brown dwarf regime. Correcting for completeness, we find a star to brown dwarf number ratio of, currently, 4:1, and an average mass per object of 0.41 M ⊙.