Exoplanets around G-K Giants

TL;DR

This study investigates the occurrence and characteristics of exoplanets around G and K giant stars using high-resolution spectroscopic data from TLS and HARPS, revealing insights into their frequency, mass, and orbital periods.

Contribution

It provides new observational evidence on the prevalence and properties of planets around giant stars, challenging previous assumptions about metallicity preferences.

Findings

At least 18% of studied giants show potential planetary signals.

Giant planets around these stars tend to be more massive and have longer orbital periods.

Planet occurrence does not seem to favor metal-rich giant stars.

Abstract

G and K giants are a class of radial velocity (RV) variables. One reason for this variability are planetary companions which are indicated in time series of stellar spectra. Since 2004 these spectra in the visual range were obtained with the high resolution coud\'e \'echelle spectrograph mounted on the 2m telescope of the Th\"uringer Landessternwarte Tautenburg (TLS) for a northern sample of 62 very bright K giants. In the South around 300 G and K giants were observed with HARPS mounted on the 3.6m telescope on La Silla. The TLS sample contains at least 11 stars (18 %) which show low-amplitude, long-period RV variations most likely due to planets. This percentage of planet frequency is confirmed by preliminary results of the HARPS study. Moreover the TLS survey seems to indicate that giant planets do not favour metal-rich stars, are more massive, and have longer periods than those found around solar-type host stars.