Institute of Astronomy

Giant Planets Around Giant Stars

SpeakerTalk DateTalk Series
Artie Hatzes29 July 2014Across HR 2014 Talks


Over the past 20 years approximately 1000 exoplanets have been discovered. More than 80% of these exoplanets orbit host stars with masses less than about 1.2 M_sun. The reason for this is that the Doppler method, the most successful detection method, has insufficient precision to detect planets around more massive main sequence stars. These stars are hot and thus have few spectral lines that are often broadened by large rotation rates. We thus know little about the process of planet formation as a function of the most fundamental property of a star its mass.

Evolved giant stars offer us a way to detect planets around intermediate mass stars. As massive stars evolve up the giant branch their effective temperatures decrease and their rotation rates slow. They thus have a plethora of narrow spectral lines amenable to Doppler measurements. A number of programs have been surveying giant stars for exoplanets. So far about 50 exoplanets have been discovered around stars with stellar masses greater than about 1.2 M_sun. Although far fewer than the number of planets around solar like stars, these planets around evolved intermediate planets show differences in properties to their main sequence counterparts. Few have been discovered in short period orbits and most are in long period orbits of several hundred days. There is also a tendency for giant planets around more massive stars to be more frequent, and with higher masses (~ 5 M_Jupiter) than for those around solar mass stars. I will review the results from these various programs as well as address such issues as determination of the stellar mass, which is more problematic than for main sequence stars, and the possibility that rotational modulation by surface features may be responsible for some of the long period radial velocity signals that have been detected.