Asteroseismology of the planet-hosting star mu Arae. II. Seismic analysis

Astrophysics, abstract
astro-ph/0503695

From: Michael Bazot [view email]

Date (v1): Thu, 31 Mar 2005 20:54:23 GMT   (62kb)

Date (revised v2): Fri, 1 Apr 2005 09:04:55 GMT   (62kb)

As most exoplanets host stars, HD 160691 (alias mu 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 (Bazot and Vauclair 2004), seismology can help
choosing between the two scenarios. This star was observed during eight nights
with the spectrograph HARPS at La Silla Observatory. Forty three p-modes have
been identified (Bouchy et al. 2005). In the present paper, we discuss the
modelisation of this star. We computed stellar models iterated to present the
same observable parameters (luminosity, effective temperature, outer chemical
composition) while the internal structure was different according to the two
extreme assumptions : original overmetallicity or accretion. We show that in
any case the seismic constraints lead to models in complete agreement with the
external parameters deduced from spectroscopy and from the Hipparcos parallax
(L and Teff). We discuss the tests which may lead to a choice between the two
typical scenarios. We show that the “small separation” seem 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 conclude. We discuss
the observations which would be needed to go further and solve this question.

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