A likely exoplanet orbiting the oscillating K-giant α Arietis^⋆

¹ Korea Astronomy and Space Science Institute, 776, Daedeokdae-Ro, Youseong-Gu, 305-348 Daejeon, Korea
e-mail bclee@kasi.re.kr; iwhan@kasi.re.kr; kmkim@kasi.re.kr;
² Crimean Astrophysical Observatory, Nauchny, 98409 Crimea, Ukraine
e-mail davidm@crao.crimea.ua
³ Department of Astronomy and Atmospheric Sciences, Kyungpook National University, 702-701 Daegu, Korea
e-mail mgp@knu.ac.kr

Received: 10 December 2010
Accepted: 10 March 2011

Abstract

Aims. To search for extrasolar planets around intermediate-mass stars, we are conducting a precise RV survey around K-giants.

Methods. We present high-accuracy RV measurements of α Ari made from November 2003 to February 2010. This star belongs to our sample of 55 K-giants studied for extrasolar 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.

Results. We find a planetary companion with long-period and low-amplitude radial velocity (RV) variations in oscillating K2 III star α Ari (HD 12929). We do not find the correlation between RV variations and chromospheric activity indicators (Ca II H & K region, Hα line). The bisector analysis also shows that the 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 = 41 m s^-1, and an eccentricity of e = 0.25 fits the data best. Assuming a possible stellar mass of M _⋆  = 1.5   M_⊙, we estimate the minimum mass for the planetary companion of m₂ sin i = 1.8 M_Jup with an orbital semi-major axis of 1.2 AU.

Conclusions. Our finding of a likely exoplanet in α Ari supports searching for extrasolar planets around giant stars with multiperiodic oscillations.