Spectroscopic characterization of a sample of metal-poor solar-type stars from the HARPS planet search program Precise spectroscopic parameters and mass estimation

Stellar metallicity strongly correlates with the presence of planets and their properties. To check for new correlations between stars and the existence of an orbiting planet, we determine precise stellar parameters for a sample of metal-poor solar-type stars. This sample was observed with the HARPS spectrograph and is part of a program to search for new extrasolar planets. The stellar parameters were determined using an LTE analysis based on equivalent widths (EW) of iron lines and by imposing excitation and ionization equilibrium. The ARES code was used to allow automatic and systematic derivation of the stellar parameters. Precise stellar parameters and metallicities were obtained for 97 low metal-content stars. We also present the derived masses, luminosities, and new parallaxes estimations based on the derived parameters, and compare our spectroscopic parameters with an infra-red flux method calibration to check the consistency of our method in metal poor stars. Both methods seems to give the same effective temperature scale. Finally we present a new calibration for the temperature as a function of B - V and [Fe/H]. This was obtained by adding these new metal poor stars in order to increase the range in metallicity for the calibration. The standard deviation of this new calibration is similar to 50 K.