Detection of a planetary companion around the giant star γ1 Leonis^*,**

¹ Korea Astronomy and Space Science Institute, 61-1, Whaam-dong, Yuseong-gu, Daejeon, 305-348, Korea e-mail: iwhan@kasi.re.kr
² Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu, 702-701, Korea
³ Astrophysical Research Center for the Structure and Evolution of the Cosmos, Sejong University, Seoul, 143-747, Korea
⁴ Crimean Astrophysical Observatory, Nauchny, Crimea, 98409, Ukraine
⁵ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁶ Observatorio Astronómico Nacional SPM, Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, BC, México

Received: 20 May 2009
Accepted: 13 October 2009

Abstract

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 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 , 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 Leonis. We conclude that the detected RV variations can be best explained by a planetary companion with an estimated mass of and a semi-major axis of a = 1.19 AU, assuming a stellar mass of 1.23 .