Overabundance ofα-elements in exoplanet-hosting stars

Abstract

We present the results for a chemical abundance analysis between planet-hosting and stars without planets for 12 refractory elements for a total of 1111 nearby FGK dwarf stars observed within the context of the HARPS GTO programs. Of these stars, 109 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-hosting and stars without planets is observed for Mg. Our data suggest that the planet incidence is greater among the thick disk population than among the thin disk for mettallicities bellow −0.3 dex. After examining the [α/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 determinating factor for that. The inspection of the Galactic orbital parameters and kinematics of the planet-hosting stars shows that Neptunian hosts tend to belong to the "thicker" disk compared to their high-mass planet-hosting counterparts. We also found that Neptunian hosts follow the distribution of high-α stars in the UW vs. V velocities space, but they are more enhanced in Mg than high-α 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 of iron is low. These results may provide strong constraints for the models of planet formation, especially for planets with low mass.

From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio

“…1 shows that stars belonging to the Galactic thick disk (the stars above the green dashed line) have higher [Mg/Si] ratio than their thin disk counterparts (below the line) 3 . Taking into account the fact that planet-hosting stars at low metallicities mostly belong to the Galactic thick disk (Haywood 2008;Adibekyan et al 2012b) one can speculate that the oldest terrestrial planetary systems (e.g. Kepler-444;Campante et al 2015) may have different compositions to the terrestrial solar system planets; however, for the exact derivation of the chemical properties of these planets precise abundances of C and O are also needed 4 .…”

The GAPS programme with HARPS-N at TNG

“…In fact, the Galactic thin and thick disks appear to overlap significantly around −0.7 < ∼ [Fe/H] < ∼ 0.0 dex when the iron abundance is used as a reference, while they are separated in [α/Fe] (see, e.g., Bensby et al 2003;Mishenina et al 2004). Here, we investigate to which population the XO-2 stellar system belongs to take advantage of 431 stars listed in the catalog by Soubiran & Girard (2005) and 906 FGK dwarf stars analyzed by Adibekyan et al (2012) with thin-disk, thick-disk, and halo membership probabilities (P thin , P thick , P halo ) higher than 90%. We used as abundance of α-elements the definition …”

The metallicity signature of evolved stars with planets

“…Adibekyan et al 2012, and references therein). An overabundance of refractory elements with respect to volatiles in MS planet hosts is considered as a possible sign of late-stage accretion, a tendency that is expected to disappear during the star evolution towards the red-giant phase.…”