Planetary companions around the K giant stars 11 UMi and HD 32518

TL;DR

This study reports the discovery of planetary companions around two K giant stars, 11 UMi and HD 32518, using precise radial velocity measurements to investigate planet formation around intermediate-mass stars.

Contribution

First detection of planetary companions around 11 UMi and HD 32518, demonstrating the effectiveness of RV surveys in studying planet occurrence around giant stars.

Findings

11 UMi hosts a planet with 10.5 Jupiter masses.

HD 32518 hosts a planet with 3.0 Jupiter masses.

No stellar activity was detected at the RV periods.

Abstract

11 UMi and HD 32518 belong to a sample of 62 K giant stars that has been observed since February 2004 using the 2m Alfred Jensch telescope of the Th\"uringer Landessternwarte (TLS) to measure precise radial velocities (RVs). The aim of this survey is to investigate the dependence of planet formation on the mass of the host star by searching for planetary companions around intermediate-mass giants. An iodine absorption cell was used to obtain accurate RVs for this study. Our measurements reveal that the RVs of 11 UMi show a periodic variation of 516.22 days. The RV curve of HD 32518 shows sinusoidal variations with a period of 157.54 days. The HIPPARCOS photometry as well as our H\alpha core flux measurements reveal no variability with the RV period. Thus, Keplerian motion is the most likely explanation for the observed RV variations for both giant stars. An exoplanet with a minimum mass of 10.5 Jupiter masses orbits the K giant 11 UMi. The K1 III giant HD 32518 hosts a planetary companion with a minimum mass of 3.0 Jupiter masses in a nearly circular orbit. These are the 4th and 5th planets published from this TLS survey.