A Planet Candidate in the Stellar Triple System HD 178911

We report the detection of a low-mass companion orbiting the solar-type star HD178911B, the distant component of the stellar triple system HD178911. The variability of HD178911B was first detected using radial-velocity measurements obtained with the HIRES spectrograph mounted on the 10-m Keck1 telescope at the W.M. Keck Observatory (Hawaii, USA). We then started an intense radial-velocity follow up of the star with the ELODIE echelle spectrograph mounted on the 1.93-m telescope at the Observatoire de Haute-Provence (France) in order to derive its orbital solution. The detected planet candidate has an orbital period of 71.5 days and a minimum mass of 6.3 Jupiter masses. We performed a spectral analysis of the star, which shows that the lithium abundances in the system are similar to those in another known planet-hosting wide binary stellar system, 16 Cyg. In both systems the lithium is undetected in the atmosphere of the visual secondary harboring the planetary companion, but is easily detected in the spectrum of the visual primary. We discuss this similarity and its ramifications.