Radial Velocity Search for Extrasolar Planets in Visual Binary Systems

Abstract We searched for extrasolar planets in visual binary systems using precise Doppler-shift measurements taken over a period of 4 yr. Using the HIgh Dispersion Echelle Spectrograph (HIDES) equipped on the Okayama Astrophysical Observatory (OAO) 188 cm reflector, we achieved a radial-velocity precision of about 10 ms$^{-1}$. We monitored both primary and secondary stars of six visual binary systems, and primary stars of three visual binaries. Among them, three objects show large radial-velocity variations. ADS 7311 A exhibits a decreasing trend in radial velocity with a best-fit slope of $-$30 ms$^{-1}$yr$^{-1}$, while 31 Dra A shows an increasing trend with a best-fit slope of $+$220 ms$^{-1}$yr$^{-1}$. These long-term trends in radial velocity may be attributable to unseen companions. BDS 10966 A shows a periodic variation in radial velocity with a period of 840 d and a semiamplitude of about 120 ms$^{-1}$, implying an association of a planetary-mass companion, rotational modulation, or nonradial oscillation of the photosphere. In any case, we should mention the nonassociation between BDS 10966 A and B, suggested by the different proper motions, radial velocities, and Hipparcos parallaxes.