A Planet Candidate in the Stellar Triple System HD 178911

We report the detection of a low-mass companion orbiting the solar-type starHD178911B, the distant component of the stellar triple system HD178911. Thevariability of HD178911B was first detected using radial-velocity measurementsobtained with the HIRES spectrograph mounted on the 10-m Keck1 telescope at theW.M. Keck Observatory (Hawaii, USA). We then started an intense radial-velocityfollow up of the star with the ELODIE echelle spectrograph mounted on the1.93-m telescope at the Observatoire de Haute-Provence (France) in order toderive its orbital solution. The detected planet candidate has an orbitalperiod of 71.5 days and a minimum mass of 6.3 Jupiter masses. We performed aspectral analysis of the star, which shows that the lithium abundances in thesystem are similar to those in another known planet-hosting wide binary stellarsystem, 16 Cyg. In both systems the lithium is undetected in the atmosphere ofthe visual secondary harboring the planetary companion, but is easily detectedin the spectrum of the visual primary. We discuss this similarity and itsramifications.Comment: 24 pages, 4 figures, 3 tables, accepted for publication in The Astrophysical Journa