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

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.

Based on archival data obtained with the SOPHIE (1.93-m telescope OHP observatory), HARPS (3.6-m ESO, La Silla-Paranal Observatory), and HARPS-N (TNG telescope, La Palma) spectrographs.Appendices are available in electronic form at http://www.aanda.org