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1. 3D Selection of 167 Substellar Companions to Nearby Stars

   https://doi.org/10.3847/1538-4365/ac7e57  

   Feng, Fabo ; Butler, R. Paul ; Vogt, Steven S. ; Clement, Matthew S. ; Tinney, C. G. ; Cui, Kaiming ; Aizawa, Masataka ; Jones, Hugh R. A. ; Bailey, J. ; Burt, Jennifer ; et al ( August 2022 , The Astrophysical Journal Supplement Series)

   We analyze 5108 AFGKM stars with at least five high-precision radial velocity points, as well as Gaia and Hipparcos astrometric data, utilizing a novel pipeline developed in previous work. We find 914 radial velocity signals with periods longer than 1000 days. Around these signals, 167 cold giants and 68 other types of companions are identified, through combined analyses of radial velocity, astrometry, and imaging data. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3%, and find a significant brown-dwarf valley around 40M_Jup. We also find a power-law distribution in the host binary fraction beyond 3 au, similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. Our work also reveals nine substellar systems (GJ 234 B, GJ 494 B, HD 13724 b, HD 182488 b, HD 39060 b and c, HD 4113 C, HD 42581 d, HD 7449 B, and HD 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. Depending on their ages, we estimate that an additional 10–57 substellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude.

    

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2. On the Unusual Variability of 2MASS J06195260–2903592: A Long-lived Disk around a Young Ultracool Dwarf

   https://doi.org/10.3847/1538-3881/ac8cee  

   Liu, Michael C. ; Magnier, Eugene A. ; Zhang, Zhoujian ; Gaidos, Eric ; Dupuy, Trent J. ; Liu, Pengyu ; Biller, Beth A. ; Vos, Johanna M. ; Allers, Katelyn N. ; Hinkle, Jason T. ; et al ( September 2022 , The Astronomical Journal)

   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 comparableA_Vchanges. 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 beA_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 0.11–0.17M_☉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.

    

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3. A Wide Planetary Mass Companion Discovered through the Citizen Science Project Backyard Worlds: Planet 9

   https://doi.org/10.3847/1538-4357/ac2499  

   Faherty, Jacqueline K. ; Gagné, Jonathan ; Popinchalk, Mark ; Vos, Johanna M. ; Burgasser, Adam J. ; Schümann, Jörg ; Schneider, Adam C. ; Kirkpatrick, J. Davy ; Meisner, Aaron M. ; Kuchner, Marc J. ; et al ( December 2021 , The Astrophysical Journal)

   Abstract Through the Backyard Worlds: Planet 9 citizen science project we discovered a late-type L dwarf co-moving with the young K0 star BD+60 1417 at a projected separation of 37″ or 1662 au. The secondary—CWISER J124332.12+600126.2 (W1243)—is detected in both the CatWISE2020 and 2MASS reject tables. The photometric distance and CatWISE proper motion both match that of the primary within ∼1 σ and our estimates for a chance alignment yield a zero probability. Follow-up near-infrared spectroscopy reveals W1243 to be a very red 2MASS ( J – K s = 2.72), low surface gravity source that we classify as L6–L8 γ . Its spectral morphology strongly resembles that of confirmed late-type L dwarfs in 10–150 Myr moving groups as well as that of planetary mass companions. The position on near- and mid-infrared color–magnitude diagrams indicates the source is redder and fainter than the field sequence, a telltale sign of an object with thick clouds and a complex atmosphere. For the primary we obtained new optical spectroscopy and analyzed all available literature information for youth indicators. We conclude that the Li i abundance, its loci on color–magnitude and color–color diagrams, and the rotation rate revealed in multiple TESS sectors are all consistent with an age of 50–150 Myr. Using our re-evaluated age of the primary and the Gaia parallax, along with the photometry and spectrum for W1243, we find T eff = 1303 ± 31 K, log g = 4.3 ± 0.17 cm s −2 , and a mass of 15 ± 5 M Jup . We find a physical separation of ∼1662 au and a mass ratio of ∼0.01 for this system. Placing it in the context of the diverse collection of binary stars, brown dwarfs, and planetary companions, the BD+60 1417 system falls in a sparsely sampled area where the formation pathway is difficult to assess. 

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4. The JWST Early-release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 μm Spectrum of the Planetary-mass Companion VHS 1256–1257 b

   https://doi.org/10.3847/2041-8213/acb04a  

   Miles, Brittany E. ; Biller, Beth A. ; Patapis, Polychronis ; Worthen, Kadin ; Rickman, Emily ; Hoch, Kielan K. ; Skemer, Andrew ; Perrin, Marshall D. ; Whiteford, Niall ; Chen, Christine H. ; et al ( March 2023 , The Astrophysical Journal Letters)

   We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b isa<20M_Jupwidely separated (∼8″,a= 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color–magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256 b with JWST's NIRSpec IFU and MIRI MRS modes for coverage from 1 to 20μm at resolutions of ∼1000–3700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the JWST spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.

    

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5. THE STRONGEST MAGNETIC FIELDS ON THE COOLEST BROWN DWARFS

   Melodie M. Kao, Gregg Hallinan ( April 2018 , Astrophysical journal)

   We have used the Jansky VLA to observe a sample of 5 known aurorally emitting late L and T dwarfs ranging in age from 0.2-3.4 Gyr. We observed each target for seven hours, extending to higher frequencies than previously attempted for objects in this sample. We establish proportionally higher limits on maximum surface magnetic field strengths while simultaneously placing constraints on rotation periods through detections of repeating pulses. Observations at 8{12 GHz yield measurements of 3.7{4.1 kG localized field strengths (corresponding to minimum mean surface fields between 2.7{2.9 kG) on four of our targets, including the archetypal cloud variable T2.5 dwarf SIMP J01365663+0933473 recently proposed to be a possible planetary-mass object in the Carina-Near moving group. We detect a circularly polarized radio pulse at 15{16.5 GHz for the T6.5 dwarf 2MASS 10475385+2124234, corresponding to a localized 5.6 kG field strength and minimum mean surface field of 4.0 kG. For the same object, we also tentatively detect a circularly polarized radio pulse at 16.5{18 GHz corresponding to a localized 6.2 kG field strength and minimum mean surface field of 4.4 kG. We measure rotation periods between 1.44-2.88 hr for all targets, supporting i) the emerging consensus in convective dynamo models that rapid rotation may be important for producing strong dipole fields and/or ii) rapid rotation is a key ingredient for driving the current systems powering auroral radio emission. We do not detect a clear cutoff in the pulsed emission for any targets, which would correspond to a maximum local surface magnetic field strength. However, we do observe evidence of variable structure in the frequency-dependent timeseries of our targets on timescales shorter than a rotation period, suggesting a higher degree of variability in the current systems near the surfaces of brown dwarfs, where emission at the highest frequencies are expected to probe. Finally, we find that old brown dwarfs may generate fields as strong as young brown dwarfs. 

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