A massive planet to the young disc star HD 81040

We report the discovery of a massive planetary companion orbiting the young disc star HD 81040. Based on five years of precise radial-velocity measurements with the HIRES and ELODIE spectrographs, we derive a spectroscopic orbit with a period P = 1001.0 days and eccentricity e = 0.53. The inferred minimum mass for the companion of m(2) sin i = 6.86 M-Jup places it in the high-mass tail of the extrasolar planet mass distribution. From the ELODIE spectra we derive a Lithium abundance of log epsilon(Li) = 1.90, and from the HIRES spectra of the cores of the Ca II H and K lines we derive an activity index of [log R'(HK)] = - 4.48, suggesting an age of about 0.8 Gyr. The radial-velocity residuals exhibit a scatter significantly larger than the typical internal measurement precision of the instruments. We attribute this excess velocity jitter to activity on the surface of the moderately young host star. However, the amplitude of the jitter is much too small and the expected period of rotation is much too short to explain the observed orbital motion, which we conclude is due to a massive planetary companion.