Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93^⋆,⋆⋆

¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: nuno@astro.up.pt
² Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
³ Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
⁴ Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
⁵ Centre for Star and Planet Formation, Natural History Museum of Denmark, Univ. of Copenhagen, 1350 Copenhagen, Denmark
⁶ SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK
⁷ Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland

Received: 29 June 2015
Accepted: 23 July 2015

Abstract

Aims. We explore the possibility that the stellar relative abundances of different species can be used to constrain the bulk abundances of known transiting rocky planets.

Methods. We use high resolution spectra to derive stellar parameters and chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass, rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same line along the mass-radius diagram, pointing toward a similar composition. The derived abundance ratios are compared with the solar values. With a simple stoichiometric model, we estimate the iron mass fraction in each planet, assuming stellar composition.

Results. We show that in all cases, the iron mass fraction inferred from the mass-radius relationship seems to be in good agreement with the iron abundance derived from the host star’s photospheric composition.

Conclusions. The results suggest that stellar abundances can be used to add constraints on the composition of orbiting rocky planets.