The HARPS search for southern extra-solar planets^*,**

IX. Exoplanets orbiting HD 100777, HD 190647, and HD 221287

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: dnaef@eso.org
² Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
³ Physikalisches Institut Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁴ Institut d'Astrophysique de Paris, UMR7095, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁵ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, 13376 Marseille 12, France
⁶ Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
⁷ Centro de Geofísica de Évora, Rua Romão Ramalho 59, 7002-554 Évora, Portugal

Received: 26 February 2007
Accepted: 11 April 2007

Abstract

Context. The HARPS high-resolution high-accuracy spectrograph was made available to the astronomical community in the second half of 2003. Since then, we have been using this instrument for monitoring radial velocities of a large sample of Solar-type stars (1400 stars) in order to search for their possible low-mass companions.

Aims. Amongst the goals of our survey, one is to significantly increase the number of detected extra-solar planets in a volume-limited sample to improve our knowledge of their orbital elements distributions and thus obtain better constraints for planet-formation models.

Methods.Radial-velocities were obtained from high-resolution HARPS spectra via the cross-correlation method. We then searched for Keplerian signals in the obtained radial-velocity data sets. Finally, companions orbiting our sample stars were characterised using the fitted orbital parameters.

Results. In this paper, we present the HARPS radial-velocity data and orbital solutions for 3 Solar-type stars: HD 100777, HD 190647, and HD 221287. The radial-velocity data of HD 100777 is best explained by the presence of a 1.16 M_Jup planetary companion on a 384-day eccentric orbit (). The orbital fit obtained for the slightly evolved star HD 190647 reveals the presence of a long-period ( d) 1.9 M_Jup planetary companion on a moderately eccentric orbit (). HD 221287 is hosting a 3.1 M_Jup planet on a 456-day orbit. The shape of this orbit is not very well-constrained because of our non-optimal temporal coverage and because of the presence of abnormally large residuals. We find clues that these large residuals result from spectral line-profile variations probably induced by processes related to stellar activity.