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

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_⊙ ) and ω Ser (G8III, 2.2 M_⊙ ) host a relatively low-mass planet with minimum masses of m₂ sini = 1.6 M_J and 1.7 M_J in nearly circular orbits with periods of P = 312 and 277 d, respectively. HD 120084 (G7 III, 2.4 M_⊙ ) hosts an eccentric planet with m₂sini = 4.5 M_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.