HIP 33609 b: An Eccentric Brown Dwarf Transiting a V=7.3 Rapidly Rotating B-Star

Abstract

We present the discovery and characterization of HIP 33609 b, a transiting warm brown dwarf orbiting a late B star, discovered by NASA's Transiting Exoplanet Survey Satellite TESS as TOI-588 b. HIP 33609 b is a large (R${}_b$ = 1.580${}_{-0.070}^{+0.074}$ R${}_J$) brown dwarf on a highly eccentric (e = 0.560${}_{-0.031}^{+0.029}$) orbit with a 39-day period. The host star is a bright (V = 7.3 mag), T${}_{eff}$ = 10,400${}_{-660}^{+800}$ K star with a mass of M${}_{\ast }$ = 2.383${}_{-0.095}^{+0.10}$ M${}_{\odot }$ and radius of R${}_{\ast }$ = 1.863${}_{-0.082}^{+0.087}$ R${}_{\odot }$, making it the hottest transiting brown dwarf host star discovered to date. We obtained radial velocity measurements from the CHIRON spectrograph confirming the companion's mass of M${}_b$ = 68.0${}_{-7.1}^{+7.4}$ M${}_J$ as well as the host star's rotation rate ($vsin{i}_{\ast }=55.6\pm 1.8$ km/s). We also present the discovery of a new comoving group of stars, designated as MELANGE-6, and determine that HIP 33609 is a member. We use a combination of rotation periods and isochrone models fit to the cluster members to estimate an age of 150 $\pm$ 25 Myr. With a measured mass, radius, and age, HIP 33609 b becomes a benchmark for substellar evolutionary models.

16 pages, 5 figures, 4 tables, Submitted to AAS Journals

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