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1. 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 allmore »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.« less
2. Discovery of 34 Low-mass Comoving Systems Using NOIRLab Source Catalog DR2

   https://doi.org/10.3847/1538-3881/ac68e7  

   Kiwy, Frank ; Faherty, Jacqueline K. ; Meisner, Aaron ; Schneider, Adam C. ; Kirkpatrick, J. Davy ; Kuchner, Marc J. ; Burgasser, Adam J. ; Casewell, Sarah ; Kiman, Rocio ; Calamari, Emily ; et al ( June 2022 , The Astronomical Journal)

   Abstract We present the discovery of 34 comoving systems containing an ultracool dwarf found by means of the NOIRLab Source Catalog (NSC) DR2. NSC’s angular resolution of ∼ 1″ allows for the detection of small separation binaries with significant proper motions. We used the catalog’s accurate proper motion measurements to identify the companions by cross-matching a previously compiled list of brown dwarf candidates with NSC DR2. The comoving pairs consist of either a very low-mass star and an ultracool companion, or a white dwarf and an ultracool companion. The estimated spectral types of the primaries are in the K and M dwarf regimes, those of the secondaries in the M, L, and T dwarf regimes. We calculated angular separations between ∼2″ and ∼ 56″, parallactic distances between ∼43 and ∼261 pc, and projected physical separations between ∼169 and ∼8487 au. The lowest measured total proper motion is 97 mas yr −1 , with the highest 314 mas yr −1 . Tangential velocities range from ∼23 to ∼187 km s −1 . We also determined comoving probabilities, estimated mass ratios, and calculated binding energies for each system. We found no indication of possible binarity for any component of the 34 systemsmore »in the published literature. The discovered systems can contribute to the further study of the formation and evolution of low-mass systems as well as to the characterization of cool substellar objects.« less
3. Precision measurement of a brown dwarf mass in a binary system in the microlensing event: OGLE-2019-BLG-0033/MOA-2019-BLG-035

   https://doi.org/10.1051/0004-6361/202243490  

   Herald, A. ; Udalski, A. ; Bozza, V. ; Rota, P. ; Bond, I. A. ; Yee, J. C. ; Sajadian, S. ; Mróz, P. ; Poleski, R. ; Skowron, J. ; et al ( July 2022 , Astronomy & Astrophysics)

   Context. Brown dwarfs are transition objects between stars and planets that are still poorly understood, for which several competing mechanisms have been proposed to describe their formation. Mass measurements are generally difficult to carry out for isolated objects as well as for brown dwarfs orbiting low-mass stars, which are often too faint for a spectroscopic follow-up. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here, we present an analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is caused by a binary system composed of a brown dwarf orbiting a red dwarf. Methods. Thanks to extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including the parallax, source radius, and orbital motion of the binary lens. Results. Following an accurate modeling process, we found that the lens is composed of a red dwarf with a mass of M 1 = 0.149 ± 0.010 M ⊙ and a brown dwarf with a mass of M 2 = 0.0463 ± 0.0031 M ⊙ at a projected separation of a ⊥ = 0.585 au. The system has a peculiar velocity that is typical ofmore »old metal-poor populations in the thick disk. A percent-level precision in the mass measurement of brown dwarfs has been achieved only in a few microlensing events up to now, but will likely become more common in the future thanks to the Roman space telescope.« less
4. The EREBOS project: Investigating the effect of substellar and low-mass stellar companions on late stellar evolution: Survey, target selection, and atmospheric parameters

   https://doi.org/10.1051/0004-6361/201936019  

   Schaffenroth, V. ; Barlow, B. N. ; Geier, S. ; Vučković, M. ; Kilkenny, D. ; Wolz, M. ; Kupfer, T. ; Heber, U. ; Drechsel, H. ; Kimeswenger, S. ; et al ( October 2019 , Astronomy & Astrophysics)

   Eclipsing post-common-envelope binaries are highly important for resolving the poorly understood, very short-lived common-envelope phase of stellar evolution. Most hot subdwarfs (sdO/Bs) are the bare helium-burning cores of red giants that have lost almost all of their hydrogen envelope. This mass loss is often triggered by common-envelope interactions with close stellar or even substellar companions. Cool companions to hot subdwarf stars such as late-type stars and brown dwarfs are detectable from characteristic light-curve variations – reflection effects and often eclipses. In the recently published catalog of eclipsing binaries in the Galactic Bulge and in the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey, we discovered 125 new eclipsing systems showing a reflection effect seen by visual inspection of the light curves and using a machine-learning algorithm, in addition to the 36 systems previously discovered by the Optical Gravitational Lesing Experiment (OGLE) team. The Eclipsing Reflection Effect Binaries from Optical Surveys (EREBOS) project aims at analyzing all newly discovered eclipsing binaries of the HW Vir type (hot subdwarf + close, cool companion) based on a spectroscopic and photometric follow up to derive the mass distribution of the companions, constrain the fraction of substellar companions, and determine the minimum mass needed to stripmore »off the red-giant envelope. To constrain the nature of the primary we derived the absolute magnitude and the reduced proper motion of all our targets with the help of the parallaxes and proper motions measured by the Gaia mission and compared those to the Gaia white-dwarf candidate catalog. It was possible to derive the nature of a subset of our targets, for which observed spectra are available, by measuring the atmospheric parameter of the primary, confirming that less than 10% of our systems are not sdO/Bs with cool companions but are white dwarfs or central stars of planetary nebula. This large sample of eclipsing hot subdwarfs with cool companions allowed us to derive a significant period distribution for hot subdwarfs with cool companions for the first time showing that the period distribution is much broader than previously thought and is ideally suited to finding the lowest-mass companions to hot subdwarf stars. The comparison with related binary populations shows that the period distribution of HW Vir systems is very similar to WD+dM systems and central stars of planetary nebula with cool companions. In the future, several new photometric surveys will be carried out, which will further increase the sample of this project, providing the potential to test many aspects of common-envelope theory and binary evolution.« less
5. Spectral library of age-benchmark low-mass stars and brown dwarfs

   https://doi.org/10.1093/mnras/stz3441  

   Manjavacas, E. ; Lodieu, N. ; Béjar, V. J. S. ; Zapatero-Osorio, M. R. ; Boudreault, S. ; Bonnefoy, M. ( December 2019 , Monthly Notices of the Royal Astronomical Society)

   In recent years, some extremely red brown dwarfs have been discovered. They were believed to have a low surface gravity, but many of their spectral characteristics are similar to those of high-surface-gravity brown dwarfs, showing that the spectral characteristics of young brown dwarfs are poorly understood. We aim to test surface-gravity indicators in late-M and early-L brown dwarf spectra using data obtained with the X-shooter spectrograph at the Very Large Telescope. We select a benchmark sample of brown dwarf members of Chamaeleon I (∼2 Myr), Upper Scorpius (5−10 Myr), the Pleiades (132 ± 27 Myr) and Praesepe (590−790 Myr) with well-constrained ages and similar metallicities. We provide a consistent spectral classification of the sample in the optical and in the near-infrared. We measure the equivalent widths of their alkali lines, finding that they have a moderate correlation with age, especially for objects with spectral types M8 and later. We use spectral indices defined in the literature to estimate surface gravity, finding that their gravity assignment is accurate for 75 per cent of our sample. We investigate the correlation between red colour and age, finding that after ∼10 Myr, the colour does not change significantly for our sample with spectral types M6.0–L3.0. In this case, the red colours might bemore »associated with circumstellar discs, ring structures, extinction, or viewing angle. Finally, we calculate the bolometric luminosity, and J and K bolometric corrections for our sample. We find that six objects are overluminous compared with other members of the same association. These objects are flagged as binary candidates by the Gaia survey.

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