Substellar companions to seven evolved intermediate-mass stars

Abstract

We report on the detections of substellar companions orbiting around seven evolved intermediate-mass stars from precise Doppler measurements at Okayama Astrophysical Observatory. oUMa (G4 II-III) is a giant with a mass of 3.1M, and hosts a planet with a minimum mass of m2sin i = 4.1MJ in an orbit with a period P = 1630 d and an eccentricity e = 0.13. This is the first planet candidate (<13MJ) ever discovered around a star more massive than 3M. o CrB (K0 III) is a 2.1M giant, and has a planet of m2sin i = 1.5MJ in a 187.8 d orbit with e = 0.19. This is one of the least-massive planets ever discovered around an ̃2M star. HD5608 (K0 IV) is an 1.6M subgiant hosting a planet of m2sin i = 1.4MJ in a 793 d orbit with e = 0.19. The star also exhibits a linear velocity trend, suggesting the existence of an outer, more massive companion. 75 Cet (G3 III:) is a 2.5M giant hosting a planet of m2sin i = 3.0MJ in a 692 d orbit with e = 0.12. The star also shows a possible additional periodicity of about 200 d and 1880 d with a velocity amplitude of ̃7-10ms-1, although these are not significant at this stage. Oph (K0 III) is a 3.0M giant, and has two brown-dwarf companions of m2sin i = 24MJ and 27MJ, in orbits with P = 530.3 d and 3190 d, and e = 0.126 and 0.17, respectively, which were independently announced by Quirrenbach, Reffert, and Bergmann (2011, AIP Conf. Proc. 1331, 102). The ratio of the periods is close to 1:6, suggesting that the companions are in mean motion resonance. We also independently confirmed planets around CrB (K0 III-IV) and HD210702 (K1 IV), which were announced by Johnson et al. (2008, ApJ, 675, 784) and Johnson et al. (2007a, ApJ, 665, 785), respectively. All of the orbital parameters we obtained are consistent with the previous results. © 2012. Astronomical Society of Japan.