Benchmark brown dwarf companions with welldetermined ages and modelindependent masses are powerful tools to test substellar evolutionary models and probe the formation of giant planets and brown dwarfs. Here, we report the independent discovery of HIP 21152 B, the first imaged brown dwarf companion in the Hyades, and conduct a comprehensive orbital and atmospheric characterization of the system. HIP 21152 was targeted in an ongoing highcontrast imaging campaign of stars exhibiting propermotion changes between Hipparcos and Gaia, and was also recently identified by Bonavita et al. (2022) and Kuzuhara et al. (2022). Our Keck/NIRC2 and SCExAO/CHARIS imaging of HIP 21152 revealed a comoving companion at a separation of 0.″37 (16 au). We perform a joint orbit fit of all available relative astrometry and radial velocities together with the HipparcosGaia proper motions, yielding a dynamical mass of
Black hole binary systems with companion stars are typically found via their xray emission, generated by interaction and accretion. Noninteracting binaries are expected to be plentiful in the Galaxy but must be observed using other methods. We combine radial velocity and photometric variability data to show that the bright, rapidly rotating giant star 2MASS J05215658+4359220 is in a binary system with a massive unseen companion. The system has an orbital period of ~83 days and nearzero eccentricity. The photometric variability period of the giant is consistent with the orbital period, indicating star spots and tidal synchronization. Constraints on the giant’s mass and radius imply that the unseen companion is
 Publication Date:
 NSFPAR ID:
 10122823
 Journal Name:
 Science
 Volume:
 366
 Issue:
 6465
 Page Range or eLocationID:
 p. 637640
 ISSN:
 00368075
 Publisher:
 American Association for the Advancement of Science (AAAS)
 Sponsoring Org:
 National Science Foundation
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