Precise radial velocities of giant stars. III. Spectroscopic stellar parameters

Abstract

Context: A radial velocity survey of about 380 G and K giant stars is ongoing at Lick observatory. For each star we have a high signal to noise ratio template spectrum, which we use to determine spectroscopic stellar parameters. Aim: The aim of this paper is to present spectroscopic stellar parameters, i.e. effective temperature, surface gravity, metallicity and rotational velocity for our sample of G and K giant stars. Methods: Effective temperatures, surface gravities and metallicities are determined from the equivalent width of iron lines. Rotational velocities are determined from the full width at half maximum (FWHM) of moderate spectral lines. A calibration between the FWHM and total broadening (rotational velocity and macro turbulence) is obtained from stars in common between our sample and the sample from Gray (1989). Results: The metallicity we derive is essentially equal to the literature values, while the effective temperature and surface gravity are slightly higher by 56 K and 0.15 dex, respectively. Our rotational velocities are comparable with the ones obtained by Gray (1989), but somewhat higher than the ones obtained by de Medeiros & Mayor (1999), consistent with the different diagnostics used. Conclusions: We are able to determine spectroscopic stellar parameters for about 380 G and K giant stars in a uniform way (112 stars are being analysed spectroscopically for the first time). For stars available in the literature, we find reasonable agreement between literature values and values determined in the present work. In addition, we show that the metallicity enhancement of companion hosting stars might also be valid for giant stars, with the planet-hosting giants being 0.13 +/- 0.03 dex (i.e. 35 +/- 10%) more metal-rich than our total sample of stars.