A planetary system and a highly eccentric brown dwarf around the giant stars HIP67851 and HIP97233

TL;DR

This study reports the discovery of a close-in planet and a highly eccentric brown dwarf orbiting giant stars, providing insights into substellar companion characteristics and their evolution around evolved stars.

Contribution

It presents the first detection of a planetary system and a highly eccentric brown dwarf around giant stars HIP67851 and HIP97233, respectively, using precision radial velocity measurements.

Findings

Inner planet HIP67851b is the closest-in known planet orbiting a giant star.

The brown dwarf HIP97233b has the highest eccentricity among known brown dwarfs around giant stars.

The outer companion's orbit is likely a super-Jupiter with an eccentricity of 0.61.

Abstract

Context: So far more than 60 substellar companions have been discovered around giant stars. These systems present physical and orbital properties that contrast to 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 HIP67851 and HIP97233 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 HIP67851 and HIP97233, respectively. The inner planet around HIP67851 has a period of 88.8 days, a projected mass of 1.4 Mjup and an eccentricity of 0.09. After Kepler 91b, HIP67851b is the closest-in known planet orbiting a giant star. Although the orbit of the outer object is not fully constrained, it is likely a super-Jupiter. The brown dwarf around HIP97233 has an orbital period of 1058.8 days, a minimum mass of 20.0 Mjup and an eccentricity of 0.61. This is the most eccentric known brown dwarf around a giant star.