A planetary companion around the K giant eps Corona Borealis

TL;DR

This study reports the detection of a planetary companion around the K giant epsilon CrB through long-term radial velocity monitoring, confirming a planet with a 417.9-day orbit and analyzing its implications.

Contribution

First detection of a planetary companion around epsilon CrB using high-resolution RV measurements, with detailed orbital parameters and discussion on stellar and planetary properties.

Findings

Planetary companion with 417.9-day orbit detected

Minimum mass of the planet is 6.7 Jupiter masses

No correlation between RV variations and stellar activity indicators

Abstract

Aims. Our aim is to search for and study the origin of the low-amplitude and long-periodic radial velocity (RV) variations in K giants. Methods. We present high-resolution RV measurements of K2 giant epsilon CrB from February 2005 to January 2012 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at the Bohyunsan Optical Astronomy Observatory (BOAO). Results. We find that the RV measurements for epsilon CrB exhibit a periodic variation of 417.9 +/- 0.5 days with a semi-amplitude of 129.4 +/- 2.0 m/s. There is no correlation between RV measurements and chromospheric activity in the Ca II H region, the Hipparcos photometry, or bisector velocity span. Conclusions. Keplerian motion is the most likely explanation, with the RV variations arising from an orbital motion. Assuming a possible stellar mass of 1.7 +/- 0.1 M_Sun for epsilon CrB, we obtain a minimum mass for the planetary companion of 6.7 +/- 0.3 M_Jup with an orbital semi-major axis of 1.3 AU and eccentricity of 0.11. We also discuss the implications of our observations for stellar metallicity versus planet occurrence rate and stellar mass versus planetary mass relations.