Spectroscopic investigation of stars on the lower main sequence ^*,**

¹ Université de Bordeaux - CNRS - Laboratoire d'Astrophysique de Bordeaux, BP 89, 33271 Floirac Cedex, France e-mail: Caroline.Soubiran@obs.u-bordeaux1.fr
² Astronomical Observatory, Odessa National University T.G. Shevchenko Park, Odessa 65014, Ukraine e-mail: tamar@deneb1.odessa.ua; serkor@skyline.od.ua
³ Observatoire Astronomique de l'Université Louis Pasteur, 11 rue de l'Université, Strasbourg, France e-mail: bienayme@astro.u-strasbg.fr

Received: 10 June 2008
Accepted: 9 July 2008

Abstract

Aims. The aim of this paper is to provide fundamental parameters and abundances with a high accuracy for a large sample of cool main sequence stars. This study is part of wider project, in which the metallicity distribution of the local thin disc is investigated from a complete sample of G and K dwarfs within 25 pc.

Methods. The stars were observed at high resolution and a high signal-to-noise ratio with the ELODIE echelle spectrograph. The were obtained with a calibration of the cross-correlation function. Effective temperatures were estimated by the line depth ratio method. Surface gravities () were determined by two methods: parallaxes and ionization balance of iron. The Mg and Na abundances were derived using a non-LTE approximation. Abundances of other elements were obtained by measuring equivalent widths.

Results. Rotational velocities, atmospheric parameters (T_eff, , [Fe/H], V_t), and Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, and Zn abundances are provided for 131 stars. Among them, more than 30 stars are active stars with a fraction of BY Dra and RS CVn type stars for which spectral peculiarities were investigated. We find the mean abundances of the majority of elements in active and nonactive stars to be similar, except for Li, and possibly for Zn and Co. The lithium is reliably detected in 54% of active stars but only in 20% of nonactive stars. No correlation is found between Li abundances and rotational velocities. A possible anticorrelation of  A(Li) with the index of chromospheric activity GrandS is observed.

Conclusions. Active and nonactive cool dwarfs show similar dependencies of most elemental ratios vs. [Fe/H]. This allows us to use such abundance ratios to study the chemical and dynamical evolution of the Galaxy. Among active stars, no clear correlation has been found between different indicators of activity for our sample stars.