Seismic analysis of the planet-hosting star μ Arae

¹ Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées, CNRS, UMR 5572, UPS, 14 Av. E. Belin, 31400 Toulouse, France e-mail: bazot@ast.obs-mip.fr
² Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, 13013 Marseille, France
³ Observatoire de Haute-Provence, 04870 Saint Michel l'Observatoire, France
⁴ Lisbon Observatory, Tapada da Ajuda, 1349-018 Lisboa, Portugal
⁵ Observatoire de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland

Received: 13 January 2005
Accepted: 5 March 2005

Abstract

Like most exoplanet host stars, HD 160691 (alias μ Ara) presents a metallicity excess in its spectrum compared to stars without detected planets. This excess may be primordial, in which case the star would be completely overmetallic, or it may be due to accretion in the early phases of planetary formation, in which case it would be overmetallic only in its outer layers. As discussed in a previous paper, seismology can help in choosing between the two scenarios. This star was observed during eight nights with the spectrograph HARPS at La Silla Observatory. Forty three p-modes were previously identified. In the present paper, we discuss the modelling of this star. We computed stellar models iterated to present the same observable parameters (luminosity, effective temperature, outer chemical composition) with differing internal structure according to the two extreme assumptions: original overmetallicity or accretion. We show that the seismic constraints lead to models in agreement with the external parameters deduced from spectroscopy and from the Hipparcos parallax (L and ). We show that the “small separation” seems to give a better fit for the accretion case than for the overmetallic case, but in spite of the very good data the uncertainties are still too large to be conclusive. We discuss the observations needed to resolve this question.