Planetary Companions to Three Evolved Intermediate-Mass Stars: HD 2952, HD 120084, and omega Serpentis

TL;DR

This paper reports the discovery of three planetary companions orbiting evolved intermediate-mass stars using precise radial velocity measurements, highlighting the detection of both low-mass and eccentric giant planets and discussing stellar oscillation effects.

Contribution

First detection of planetary companions around three evolved intermediate-mass stars, including a highly eccentric planet, using high-precision radial velocity techniques.

Findings

HD 2952 and omega Ser host low-mass planets in nearly circular orbits.

HD 120084 hosts a highly eccentric giant planet.

Stellar oscillations can be averaged out to detect smaller planets around giants.

Abstract

We report the detections of planetary companions orbiting around three evolved intermediate-mass stars from precise radial velocity measurements at Okayama Astrophysical Observatory. HD 2952 (K0III, 2.5 M_sun) and omega Ser (G8III, 2.2 M_sun) host a relatively low mass planet with minimum mass of m_2sin i=1.6 M_J and 1.7 M_J in nearly circular orbits with period of P=312 and 277 d, respectively. HD 120084 (G7 III, 2.4 M_sun) hosts an eccentric planet with m_2sin i=4.5 M_J in an orbit with P=2082 d and eccentricity of e=0.66. The planet has one of the largest eccentricities among those ever discovered around evolved intermediate-mass stars, almost all of which have eccentricity smaller than 0.4. We also show that radial velocity variations of stellar oscillations for G giants can be averaged out below a level of a few m/s at least in timescale of a week by high cadence observations, which enables us to detect a super-Earth and a Neptune-mass planet in short-period orbits even around such giant stars.