Evidence of a sub-stellar companion around HD 47536

Abstract

We report evidence of a low-mass companion around the K1 III giant star HD 47536. This star belongs to our sample of 83 subgiant and giant stars studied for their radial velocity variations using the FEROS spectrograph at the 1.52 m-ESO telescope on La Silla. We find that the radial velocity of HD 47536 exhibits a periodic variation of about 712 days with a semi-amplitude of 113 m s-1. These variations are not accompanied by variations in either Ca II emission or in the spectral line shapes. A Keplerian orbit due to a sub-stellar companion is thus the most viable explanation for the radial velocity variation. Assuming a moderate stellar mass of m1 = 1.1-3.0 M⊙ we obtain a minimum mass for the companion of m2 sin i = 5.0-9.7 MJup, an orbital semi-major axis of 1.6-2.3 AU, and an eccentricity of e = 0.2.