Letter to the Editor

The exoplanet-host star ι Horologii: an evaporated member of the primordial Hyades cluster

¹ Laboratoire d'Astrophysique de Toulouse-Tarbes, CNRS, Université de Toulouse, 14 Av. Ed. Belin, 31400 Toulouse, France e-mail: svcr@ast.obs-mip.fr
² Institut d'Astrophysique de Paris, 75014 Paris, France
³ Centro de Astrophysica da Universidade do Porto, Porto, Portugal

Received: 30 December 2007
Accepted: 4 March 2008

Abstract

Aims. We show that the exoplanet-host star iota Horologii, alias HD 17051, which belongs to the so-called Hyades stream, was formed within the primordial Hyades stellar cluster and has evaporated towards its present location, 40 pc away.

Methods. This result has been obtained unambiguously by studying the acoustic oscillations of this star, using the HARPS spectrometer in La Silla Observatory (ESO, Chili).

Results. Besides the fact that ι Hor belongs to the Hyades stream, we give evidence that it has the same metallicity, helium abundance, and age as the other stars of the Hyades cluster. They were formed together, at the same time, in the same primordial cloud.

Conclusions. This result has strong implications for theories of stellar formation. It also indicates that the observed overmetallicity of this exoplanet-host star, about twice that of the Sun, is original and not caused by planet accretion during the formation of the planetary system.