A planetary system and a highly eccentric brown dwarf around the giant stars HIP 67851 and HIP 97233

Abstract

Context. So far more than 60 substellar companions have been discovered around giant stars. These systems present physical and orbital properties that contrast with those detected orbiting less evolved stars.

Aims. We are conducting a radial velocity survey of 166 bright giant stars in the southern hemisphere. The main goals of our project are to detect and characterize planets in close-in orbits around giant stars in order to study the effects of the host star evolution on their orbital and physical properties.

Methods. We have obtained precision radial velocities for the giant stars HIP 67851 and HIP 97233 that have revealed periodic signals, which are most likely induced by the presence of substellar companions.

Results. We present the discovery of a planetary system and an eccentric brown dwarf orbiting the giant stars HIP 67851 and HIP 97233, respectively. The inner planet around HIP 67851 has a period of 88.8 days, a projected mass of 1.4 M-J and an eccentricity of 0.09. HIP 67851 b is one the few known planets orbiting a giant star interior to 0.5 AU. Although the orbit of the outer object is not fully constrained, it is likely a super-Jupiter. The brown dwarf around HIP 97233 has an orbital period of 1058.8 days, a minimum mass of 20.0 M-J and an eccentricity of 0.61. This is the most eccentric known brown dwarf around a giant star.