Chemical composition of 90 F and G disk dwarfs ^*,**

¹ Institute of Physics and Astronomy, University of Aarhus, DK–8000 Aarhus C, Denmark
² Department of Astronomy, Beijing Normal University, Beijing 100875, PR China
³ Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, PR China
⁴ Department of Geophysics, Peking University, Beijing 100871, PR China

Send offprint request to: P.E. Nissen, e-mail: pen@obs.aau.dk

Received: 7 October 1999
Accepted: 19 November 1999

Abstract

High resolution, high S/N spectra have been obtained for a sample of 90 F and G main-sequence disk stars covering the metallicity range , and have been analysed in a parallel way to the work of Edvardsson et al. (1993a) in order to re-inspect their results and to reveal new information on the chemical evolution of the Galactic disk.
Compared to Edvardsson et al. the present study includes several improvements. Effective temperatures are based on the Alonso et al. (1996) calibration of color indices by the infrared flux method and surface gravities are calculated from Hipparcos parallaxes, which also allow more accurate ages to be calculated from a comparison of M_V and  with isochrones. In addition, more reliable kinematical parameters are derived from Hipparcos distances and proper motions in combination with accurate radial velocities. Finally, a larger spectral coverage,  Å, makes it possible to improve the abundance accuracy by studying more lines and to discuss several elements not included in the work of Edvardsson et al.
The present paper provides the data and discusses some general results of the abundance survey. A group of stars in the metallicity range of having a small mean Galactocentric distance in the stellar orbits, R_m kpc, are shown to be older than the other disk stars and probably belong to the thick disk. Excluding these stars, a slight decreasing trend of  with increasing R_m and age is found, but a large scatter in  (up to 0.5 dex) is present at a given age and R_m. Abundance ratios with respect to Fe show, on the other hand, no significant scatter at a given . The derived trends of O, Mg, Si, Ca, Ti, Ni and Ba as a function of  agree rather well with those of Edvardsson et al., but the overabundance of Na and Al for metal-poor stars found in their work is not confirmed. Furthermore, the Galactic evolution of elements not included in Edvardsson et al., K, V and Cr, is studied. It is concluded that the terms “α elements" and “iron-peak elements" cannot be used to indicate production and evolution by specific nucleosynthesis processes; each element seems to have a unique enrichment history.