Friday, February 17, 2017

HIP 67537B: A Brown Dwarf in an Eccentric Orbit


Jones et al


We report the discovery of a substellar companion around the giant star HIP67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP67537 b: mbsini = 11.1 ± 0.6 MJ, a = 5.0 ± 0.2 AU and e = 0.59 ± 0.04. Considering random inclination angles, this object has ≳ 65% probability to be above the theoretical deuterium-burning limit, thus it is one of the few known objects in the planet to brown-dwarf transition region. In addition, we analyzed the Hipparcos astrometric data of this star, from which we derived a minimum inclination angle for the companion of 3 degrees. This value corresponds to an upper mass limit of 0.22 M⊙, therefore the probability that HIP67537 b is stellar in nature is only ∼ 6%. The large mass of the host star and the high orbital eccentricity makes HIP67537 b a very interesting and rare substellar objects. This is the second companion in the "brown dwarf desert" among our sample of EXPRESS intermediate-mass stars, corresponding to a detection fraction of f = 1.6+2.0−0.5%. This value is larger than the fraction observed in solar-type stars, providing further observational evidence of the enhanced formation efficiency of very massive planets and low-mass brown dwarfs in massive disks. Finally, we speculate about different formation channels for objects like HIP67537 b and HIP97233 b

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