Detection of a Planetary Companion around the giant star γ1 Leo

Aims. Our primary goal is to search for planets around intermediate mass stars. We are also interested in studying the nature of radial velocity (RV) variations of K giant stars. Methods. We selected about 55 early K giant (K0- K4) stars brighter than fifth magnitude that were observed using BOES, a high resolution spectrograph attached to the 1.8 m telescope at BOAO (Bohyunsan Optical Astronomy Observatory). BOES is equipped with I2 absorption cell for high precision RV measurements. Results. We detected a periodic radial velocity variations in the K0 III star γ1 Leo with a period of P = 429 days. An orbital fit of the observed RVs yields a period of P = 429 days, a semi-amplitude of K = 208 m s−1, and an eccentricity of e = 0.14. To investigate the nature of the RV variations, we analyzed the photometric, Ca II λ 8662 equivalent width, and line-bisector variations of γ1 Leo. We conclude that the detected RV variations can be best explained by a planetary companion with an estimated mass of m sin i = 8.78MJupiter and a semi-major axis of a = 1.19 AU, assuming a stellar mass of 1.23 M. Key words. Stars: K-giants–stars:exoplanets–stars:individual:γ1 Leo 1