Extrasolar planets around intermediate mass stars

A P Hatzes
Phys. Scr. 2008

Hatzes begins by reasserting the possibility of a planet around Aldeberan, alpha Tauri. It was one of the first prospective planets along with Pollux and Arcturus (Beta Gem and Alpha Boo). Pollux was later confirmed to have a planet, but neither of the others has been confirmed. If Aldrberan had a planet, it would have a 645 day orbit and M sini = 9.5 Jupiter masses.

Solving the problem of not knowing red giant's masses reliably, they calculated Aldeberan's mass using interferometric measurements of the radius and spectroscopic measurements of the surface gravity. Another method that can be used to determine stellar mass is that usually nasty stellar oscillations. Stellar oscillations are still extremely nasty, and Hatzes quoted the oscillation of a fundemental radial mode with intensity of 150m/s and said that giant stars can have intrinsic variability up to 100m/s.

In 2008 when Hatzes wrote this paper, there had been 20 extrasolar planets around giant or sub-giant stars, enough that he analyzed the trends. They exist in a limited range of period from 160-1000 days, with 1000 days appearing probably from the length of contemporary surveys. Inner planets are probably eliminated either by tthe expansion of the star's radius or new instabilities. 60% of the planets had masses over 5 Mjup, in comparison to less than 20% for normal stars. More massive star means more massive planet. He also found that the distribution of orbital eccentricities is independent of stellar mass. As he had fewer data points, he stated that a uniform planeticity-metallicity distribution was consistent with the data and that many of the planet hosting giant stars are actually metal poor.