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

TL;DR

This study demonstrates that the exoplanet-host star iota Horologii originated from the Hyades cluster and has since migrated, with its properties indicating an original overmetallicity unrelated to planet accretion.

Contribution

It provides the first clear evidence linking an exoplanet-host star to its primordial cluster through asteroseismology, revealing its formation history and original metallicity.

Findings

iota Horologii formed in the Hyades cluster

It shares the same age and composition as Hyades stars

Its overmetallicity is primordial, not due to planet accretion

Abstract

We show that the exoplanet-host star iota Horologii, alias HD17051, 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. This result has been obtained unambiguously by studying the acoustic oscillations of this star, using the HARPS spectrometer in La Silla Observatory (ESO, Chili). Besides the fact that $\iota$ 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. 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.