Evolved Exoplanet Host Stars eat Their Close-in Planets

Giant planets around two intermediate-mass evolved stars and confirmation of the planetary nature of HIP67851 c

Authors:

Jones et al

Abstract:

Precision radial velocities are required to discover and characterize planets orbiting nearby stars. Optical and near infrared spectra that exhibit many hundreds of absorption lines can allow the m/s precision levels required for such work. However, this means that studies have generally focused on solar-type dwarf stars. After the main-sequence, intermediate-mass stars (former A-F stars) expand and rotate slower than their progenitors, thus thousands of narrow absorption lines appear in the optical region, permitting the search for planetary Doppler signals in the data for these types of stars. We present the discovery of two giant planets around the intermediate-mass evolved star HIP 65891 and HIP 107773. The best Keplerian fit to the HIP 65891 and HIP 107773 radial velocities leads to the following orbital parameters: P=1084.5 d; mbsini = 6.0 Mjup; e=0.13 and P=144.3 d; mbsini = 2.0 Mjup; e=0.09, respectively. In addition, we confirm the planetary nature of the outer object orbiting the giant star HIP67851. The orbital parameters of HIP 67851c are: P=2131.8 d, mcsini = 6.0 Mjup and e=0.17. With masses of 2.5 M⊙ and 2.4 M⊙ HIP 65891 and HIP 107773 are two of the most massive stars known to host planets. Additionally, HIP67851 is one of five giant stars that are known to host a planetary system having a close-in planet (less than 0.7 AU). Based on the evolutionary states of those five stars, we conclude that close-in planets do exist in multiple systems around subgiants and slightly evolved giants stars, but probably they are subsequently destroyed by the stellar envelope during the ascent of the red giant branch phase. As a consequence, planetary systems with close-in objects are not found around horizontal branch stars.