2017A&A...602A..58J

We report the discovery of a substellar companion around the giant star HIP 67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP 67537 b: m_bsini=11.1^+0.4_–1.1M_jup, a=4.9^+0.14_–0.13AU and e=0.59^+0.05_–0.02. 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 (BD) 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 ∼2°. This value corresponds to an upper mass limit of ∼0.3M_☉, therefore the probability that HIP 67537 b is stellar in nature is ≤7%. The large mass of the host star and the high orbital eccentricity makes HIP 67537 b a very interesting and rare substellar object. This is the second candidate companion in the brown dwarf desert detected in the sample of intermediate-mass stars targeted by the EXoPlanets aRound Evolved StarS (EXPRESS) radial velocity program, which corresponds to a detection fraction of f=^+2.0_–0.5%. This value is larger than the fraction observed in solar-type stars, providing new observational evidence of an enhanced formation efficiency of massive substellar companions in massive disks. Finally, we speculate about different formation channels for this object.