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CNO behaviour in planet-harbouring stars. II. Carbon abundances in stars with and without planets using the CH band

L. SuŠrez-Andrťs, G. Israelian, J. I. GonzŠlez HernŠndez, V. Zh. Adibekyan, E. Delgado Mena, N. C. Santos, S. G. Sousa

Abstract
Context. Carbon, oxygen and nitrogen (CNO) are key elements in stellar formation and evolution, and their abundances should also have a significant impact on planetary formation and evolution. Aims. We present a detailed spectroscopic analysis of 1110 solar-type stars, 143 of which are known to have planetary companions. We have determined the carbon abundances of these stars and investigate a possible connection between C and the presence of planetary companions. Methods. We used the HARPS spectrograph to obtain high-resolution optical spectra of our targets. Spectral synthesis of the gonza band at 4300AA was performed with the spectral synthesis codes MOOG and FITTING.

Results. We have studied carbon in several reliable spectral windows and have obtained abundances and distributions that show that planet host stars are carbon rich when compared to single stars, a signature caused by the known metal-rich nature of stars with planets. We find no different behaviour when separating the stars by the mass of the planetary companion.

Conclusions. We conclude that reliable carbon abundances can be derived for solar-type stars from the CH band at 4300AA. We confirm two different slope trends for [C/Fe] with [Fe/H] because the behaviour is opposite for stars above and below solar values. We observe a flat distribution of the [C/Fe] ratio for all planetary masses, a finding that apparently excludes any clear connection between the [C/Fe] abundance ratio and planetary mass.

Keywords
stars: abundances; stars: chemically peculiar; planetary systems; Astrophysics - Solar and Stellar Astrophysics

Astronomy and Astrophysics
Volume 599, Article Number A96
2017 March

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda√ß√£o para a Ci√™ncia e a Tecnologia
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