Mixing processes in Red-Giant Stars

In a collaboration lead by Grazina Tautvaisiene, Vilnius, we are systematically studying the mixing processes in red-giants and horizontal-branch stars. We are using high-resolution spectra from the SOFIN spectrograph of the 2.5m Nordic Optical Telescope.

The first sub-project has recently been published ( Tautvaisiene et al. 2000, A&A, in press, astro-ph/0006001), and it is a study of 6 clump stars and 3 red giants in the old open cluster M67. We show that the metallicity of the cluster is solar, and that the ratios of heavy elements are as well. In the giants, the 12C/13C abundance ratio is 24+-4, while in the clump stars it has been lowered to 16+-4. Similarly, the C/N ratios have decreased from 1.7+-0.2 to 1.4 +-0.2 in the clump stars. Also the sodium abundances appear to be higher than in the solar-metallicity disk dwarf stars.

We have recently obtained spectra of 10 field-RGB and clump stars and are now making a similar investigation for those.

Latest update: June 2, 2000