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

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.

Accepted for publication in A&A

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• The Pan-Pacific Planet Search. II. Confirmation of a two-planet system around HD 121056
• The Masses of a Sample of Radial-Velocity Exoplanets with Astrometric Measurements
• Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star
• Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system
• Automated approach to measure stellar inclinations: validation through large-scale measurements on the red giant branch
• Discovery of an inflated hot Jupiter around a slightly evolved star TOI-1789
• Exoplanets Around Red Giants: Distribution and Habitability