An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4 M giant star HIP 67537
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: mb sin i 11.1+0.4 1.1Mjup, a =4.9+0.14 0.13 AU 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 deg. This value corresponds to an upper mass limit of ~0.3 M, 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.