Distribution of refractory and volatile elements in CoRoT exoplanet host stars

Abstract

The relative distribution of abundances of refractory, intermediate, and volatile elements in stars with planets can be an important tool for investigating the internal migration of a giant planet. This migration can lead to the accretion of planetesimals and the selective enrichment of the star with these elements. We report on a spectroscopic determination of the atmospheric parameters and chemical abundances of the parent stars in transiting planets . Adding data for CoRoT-3 and CoRoT-5 from the literature, we find a flat distribution of the relative abundances as a function of their condensation temperatures. For CoRoT-2, the relatively high lithium abundance and intensity of its Li i resonance line permit us to propose an age of 120 Myr, making this star one of the youngest stars with planets to date. We introduce a new methodology to investigate a relation between the abundances of these stars and the internal migration of their planets. By simulating the internal migration of a planet in a disk formed only by planetesimals, we are able, for the first time, to separate the stellar fractions of refractory, intermediate, and volatile rich planetesimals accreting onto the central star. Intermediate and volatile element fractions enriching the star are similar and much larger than those of pure refractory ones. This result is opposite to what has been considered in the literature for the accreting self-enrichment processes of stars with planets. We also show that these results are highly dependent on the model adopted for the disk distribution regions in terms of refractory, intermediate, and also volatile elements and other parameters considered. We note however, that this self-enrichment mechanism is only efficient during the first 20-30 Myr or later in the lifetime of the disk when the surface convection layers of the central star for the first time attain its minimum size configuration.

Effect of episodic accretion on the structure and the lithium depletion of low-mass stars and planet-hosting stars

“…Independent of the source of this peculiar abundance pattern, the signature of such condensation/accretion processes will still leave a greater imprint if the star convective envelope is considerably smaller than usually expected for solar type stars at ages <10 Myr. Also, the analysis of Chavero et al (2010) reveals no obvious correlation between abundances and condensation temperatures in the CoRoT stars, indicating no sign of overabundance of volatiles relative to refractories in stars harboring close-in giant planets compared to the Sun, contradicting the observations of Melendez et al (2009) and Ramirez et al (2009). The peculiar abundance ratio determinations in the Sun and solar analogs without detected giant planets must thus be confirmed by further studies.…”

“…Although interesting, however, this interpretation of the peculiar refractory to volatile abundance ratio in the Sun and other solar twins without detected close-in giant planets as a consequence of terrestrial planet formation is challenged by the recent analysis of Chavero et al (2010), based on four CoRoT planet host stars. This work suggests that alteration of abundances of refractories with respect to volatiles in stellar atmospheres may simply result from condensation processes in the accretion disk and from accretion of such altered gas onto the star.…”

Homogeneous photospheric parameters and C abundances in G and K nearby stars with and without planets

“…nitrogen, oxygen, and some refractory metals, would also expand the analysis to a larger context. Indeed, the investigation of volatile and refractory elements with respect to the distribution of their abundances in function of the condensation temperature (T C ) will shed light on recent controversies aroused by Chavero et al (2010). The flat distribution found by these authors should be confirmed with more precise abundance determination for T C 300 K (which includes C, N, and O).…”

Stellar parameters and chemical abundances of 223 evolved stars with and without planets

“…The abundance computation was done using the MOOG program (abfind driver) in combination with the LTE Kurucz model atmosphere previously calculated with FUNDPAR. The line-list and atomic parameters for most of the elements were compiled from Neves et al (2009) and from Chavero et al (2010) for Zn and Ba. We emphasize that for ions such as Na, Mg, Al, Sc i, Cr ii, Zn and Ba ii the line-list comprises only two or three lines and therefore the conclusions involving these species should be taken with caution.…”