February 8
Abstract:
Studies of the planet abundance as a function of stellar mass have shown a strong increase in the frequency of planet occurrence around stars more massive than 1.5 Msun, and that such stars are deficit in short period planets. These planet searches have relied on giant stars for a sample of high mass stars, which are hostile to precision Doppler measurements while on the main sequence due to rotation and activity. However, the observationally inferred mass for exoplanet hosting giants is inconsistent with the expected masses of a sample of field giants. These stars are more likely to have originated from a main sequence population of late F/early G dwarfs with mass 1.0-1.2 Msun, only slightly more more massive than the typical FGK dwarfs with Doppler detected planets. The erroneous mass determinations most likely arise from the extrapolation of solar-calibrated mixing length theory to the red giant branch, and suggests that the isochrones need revision with a slightly larger mixing length on the red giant branch. The deficit of short period planets is most likely explained by tidal capture. The planet abundance increase requires either a high rate of false positives in giant stars due to signals of stellar origin or a new mechanism to migrate planets inwards during the post main sequence evolution of the host star.