V. Zh. Adibekyan, N. C. Santos, S. G. Sousa, G. Israelian, E. Delgado Mena, J. I. Gonzalez Hernandez, M. Mayor, C. Lovis, S. Udry
We present the results for a chemical abundance analysis between the planet host and non-host stars for 12 refractory elements for a total of 1111 nearby FGK dwarf stars observed within the context of the HARPS GTO programs. 109 of these stars are known to harbour high-mass planetary companions and 26 stars are hosting exclusively Neptunians and super-Earths. We found that the [X/Fe] ratios for Mg, Al, Si, Sc, and Ti both for giant and low-mass planet hosts are systematically higher than those of comparison stars at low metallicities ([Fe/H] < from -0.2 to 0.1 dex depending on the element). The most evident discrepancy between planet host and non-host stars is observed for Mg. Our data suggest that the planet incidence is greater among the thick disc population than among the thin disc for mettallicities bellow -0.3 dex. After examining the [alpha/Fe] trends of the planet host and non-host samples we conclude that a certain chemical composition, and not the Galactic birth place of the stars, is the determinative factor for that. The inspection of the Galactic orbital parameters and kinematics of the planet host stars shows that Neptunian hosts tend to belong to the "thicker" disc compared to their high-mass planet hosting counterparts. We also found that Neptunian hosts follow the distribution of high-alpha stars in the UW vs V velocities space, but they are more enhanced in Mg than high-alpha stars without planetary companions. Our results indicate that some metals other than iron may also have an important contribution to planet formation if the amount
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http://arxiv.org/abs/1205.6670
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