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Description
To search for extra-solar planets around intermediate mass stars, we are conducting a precise RV survey around K-giants. We present high-accuracy RV measurements of alpha Ari from November 2003 to February 2010. This star belongs to our sample of 55 K-giants studied for extra-solar planet and pulsation searches using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) attached to the 1.8-m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We find a planetary companion with a long-period and low-amplitude radial velocity (RV) variations in oscillating K2 III star alpha Ari (HD 12929). We do not find the correlation between RV variations and chromospheric activity indicators (CaII H & K region, H{alpha} line). The bisector analysis also shows that bisector velocity span (BVS) does not show any obvious correlation with RV variation but has periodic component that may be attributed to the rotation of the star. If the RV variation is indeed caused by a planetary companion, an orbital solution with a period of P=381-days, a semi-amplitude of K=41m/s, and an eccentricity of e=0.25 fits the data best. Assuming a possible stellar mass of M_star_=1.5M_{sun}_, we estimate the minimum mass for the planetary companion of m_2_sini=1.8M_{Jupiter}_ with an orbital semi-major axis of 1.2AU. Our finding of a likely exoplanet in alpha Ari gives a support to search for extra-solar planets around giant stars with multi-periodic oscillations.
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