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

Abstract

Abstract We report on the detections of planetary companions orbiting around three evolved intermediate-mass stars based on precise radial velocity measurements at Okayama Astrophysical Observatory. HD 2952 (K0III, 2.5 $M_{\odot}$) and $\omega$ Ser (G8III, 2.2 $M_{\odot}$) host a relatively low-mass planet with minimum masses of $m_2$ sin$i =$ 1.6 $M_{\rm J}$ and 1.7 $M_{\rm J}$ in nearly circular orbits with periods of $P =$ 312 and 277 d, respectively. HD 120084 (G7 III, 2.4 $M_{\odot}$) hosts an eccentric planet with $m_2$ sin$i =$ 4.5 $M_{\rm J}$ in an orbit with $P =$ 2082 d and an 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 an eccentricity smaller than 0.4. We also show that the radial-velocity variations of stellar oscillations for G giants can be averaged out below a level of a few m s$^{-1}$, at least on a timescale of a week by high-cadence observations. This enables us to detect a super-Earth and a Neptune-mass planet in short-period orbits even around such giant stars.