A massive planet to the young disc star HD 81040

¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: asozzett@cfa.harvard.edu
² INAF – Osservatorio Astronomico di Torino, 10025 Pino Torinese, Italy
³ Observatoire de Genève, 51 Ch. de Maillettes, 1290 Sauveny, Switzerland
⁴ School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
⁵ Department of Geophysics and Planetary Sciences, Beverly and Raymond Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69678, Israel
⁶ Laboratoire d'Astrophysique de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble, France
⁷ European Southern Observatory, 3107 Alonso de Cordova, Casilla 19001, Santiago 19, Chile
⁸ Observatoire de Haute-Provence, 04870 St-Michel l'Observatoire, France

Received: 5 October 2005
Accepted: 23 November 2005

Abstract

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 days and eccentricity . The inferred minimum mass for the companion of   places it in the high-mass tail of the extrasolar planet mass distribution. From the ELODIE spectra we derive a Lithium abundance of , and from the HIRES spectra of the cores of the Ca II H and K lines we derive an activity index of , 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.