Is there plenty of metal-poor stars with planets in the Galactic thick disk?

V. Zh. Adibekyan, N. C. Santos, S. G. Sousa, G. Israelian, P. Figueira

Abstract.
We performed a uniform spectroscopic analysis of 1111 FGK dwarfs observed as part of the HARPS GTO planet search program. Elemental abundances of refractory elements are determined for the sample stars using a differential LTE analysis relative to the Sun. We applied a purely chemical approach, based on [alpha/Fe] ratio, to distinguish the various stellar components in the Galaxy. Apart from the well known Galactic thick and thin disks, we separated an alpha-enhanced stellar family at super-solar metallicity. The metal-rich high-alpha stars have orbits similar to the thin disk stars, but they are similar to thick disk stars in terms of age. Our data indicates that the incidence of stars with planets are greater among the chemically separated thick disc stars with [Fe/H] < -0.3 dex than they are among thin disk stars in the same [Fe/H] interval. However, this paucity of metal-poor exoplanet hosts in the thin disk disappears when we consider the mass abundance of Mg, Si, and Fe, instead of [Fe/H]. Additionally, we found that all the metal-poor planet hosts in the thick disk have also higher [X/Fe] ratios compared to the stars without any known planetary-mass companions in the thick and thin disks. The result is consistent with the expectations, since high [alpha/Fe] ratio means higher “global metallicity” and allows to suppose that in general, metals other than iron (especially, most abundant alpha-elements) may have an important contribution to planet formation.

New Quests in Stellar Astrophysics III. A Panchromatic View of Solar-like Stars, With and Without Planets
Puerto Vallarta, Mexico
March 2012

Type: Poster