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Centro de Astrofísica da Universidade do Porto

New and updated stellar parameters for 90 transit hosts
The effect of the surface gravity

A. Mortier, N. C. Santos, S. G. Sousa, J. M. Fernandes, V. Zh. Adibekyan, E. Delgado Mena, M. Montalto, G. Israelian

Abstract
Context. Precise stellar parameters are crucial in exoplanet research for correctly determining the planetary parameters. For stars hosting a transiting planet, determining the planetary mass and radius depends on the stellar mass and radius, which in turn depend on the atmospheric stellar parameters. Different methods can provide different results, which leads to different planet characteristics.
Aims. In this paper, we use a uniform method to spectroscopically derive stellar atmospheric parameters, chemical abundances, stellar masses, and stellar radii for a sample of 90 transit hosts. Surface gravities are also derived photometrically using the stellar density as derived from the light curve. We study the effect of using these different surface gravities on the determination of the chemical abundances and the stellar mass and radius.
Methods. A spectroscopic analysis based on Kurucz models in local thermodynamical equilibrium was performed through the MOOG code to derive the atmospheric parameters and the chemical abundances. The photometric surface gravity was determined through isochrone fitting and the use of the stellar density, directly determined from the light curve. Stellar masses and radii are determined through calibration formulae.
Results. Spectroscopic and photometric surface gravities differ, but this has very little effect on the precise determination of the stellar mass in our spectroscopic analysis. The stellar radius, and hence the planetary radius, is most affected by the surface gravity discrepancies. For the chemical abundances, the difference is, as expected, only noticable for the abundances derived from analyzing lines of ionized species.

Keywords
stars: fundamental parameters – stars: abundances – planets and satellites: fundamental parameters – techniques: spectroscopic

Notes
The data presented herein are based on observations collected at the La Silla Paranal Observatory, ESO (Chile) with the FEROS spectrograph at the 2.2-m telescope (ESO runs ID 088.C-0892, 089.C-0444, 090.C-0146) and the HARPS spectrograph at the 3.6-m telescope (ESO archive), the Paranal Observatory, ESO (Chile) with the UVES spectrograph at the VLT Kueyen telescope (ESO run ID 083.C-0174), at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias with the FIES spectrograph at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden (program ID 40-203), and at the Observatoire de Haute-Provence (OHP, CNRS/OAMP), France with the SOPHIE spectrographs at the 1.93-m telescope (program ID 11B.DISC.SOUS).
Table 4 is available in electronic form at http://www.aanda.org
Full Table 5 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A106

Astronomy and Astrophysics
Volume 558, Page A106_1
October 2013

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