Detection of a planetary companion around the giant star gamma(1) Leonis

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 I-2 absorption cell for high precision RV measurements. Results. We detected a periodic radial velocity variations in the K0 III star gamma(1) Leonis 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 lambda 8662 equivalent width, and line-bisector variations of gamma(1) Leonis. We conclude that the detected RV variations can be best explained by a planetary companion with an estimated mass of m sin i = 8.78 M-Jupiter and a semi-major axis of a = 1.19 AU, assuming a stellar mass of 1.23 M-circle dot.