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 as TOI-588 b. HIP 33609 b is a large (R b = R J) brown dwarf on a highly eccentric (e = ) orbit with a 39 days period. The host star is a bright (V = 7.3 mag), T eff = 10,400 K star with a mass of M * = M ⊙ and radius of R * = R ⊙, 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 = M J as well as the host star's rotation rate ( km s−1). 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 ± 25 Myr. With a measured mass, radius, and age, HIP 33609 b becomes a benchmark for substellar evolutionary models.