Hats-70b: A 13 MJ Brown Dwarf Transiting an A Star



We report the discovery of HATS-70b, a transiting brown dwarf at the deuterium burning limit. HATS-70b has a mass of M_{p} = 12.9{{-1.6}^{+1.8} M_{Jup} and a radius of R_{p} = 1.384_{{-0.074} {+0.079}} R_{Jup}, residing in a close-in orbit with a period of 1.89 days. The host star is a M⁎ = 1.78 ± 0.12 M_⊙ A star rotating at v sin I⁎ = 40.61{{-0.35}}^{+0.32}} km s⁻¹ , enabling us to characterize the spectroscopic transit of the brown dwarf via Doppler tomography. We find that HATS-70b, like other massive planets and brown dwarfs previously sampled, orbits in a low projected-obliquity orbit with λ = {{8.9}^{5.6°}}. The low obliquities of these systems is surprising given all brown dwarf and massive planets with obliquities measured orbit stars hotter than the Kraft break. This trend is tentatively inconsistent with dynamically chaotic migration for systems with massive companions, though the stronger tidal influence of these companions makes it difficult to draw conclusions on the primordial obliquity distribution of this population. We also introduce a modeling scheme for planets around rapidly rotating stars, accounting for the influence of gravity darkening on the derived stellar and planetary parameters.



Astronomical spectroscopy, Astronomical photometry, Extrasolar planets, Planets, Stellar dynamics, Extrasolar planets



©2019 American Astronomical Society