Processes at the turnoff

Details Processes at the turnoff Processes at the turnoff

Jan 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005hia....13..153m&link_type=abstract

In: Highlights of Astronomy, Vol. 13, as presented at the XXVth General Assembly of the IAU - 2003 [Sydney, Australia, 13 - 26 J

Astronomy and Astrophysics

Astronomy

Globular Clusters, Element Abundances

Scientific paper

Stellar evolution models taking into account atomic diffusion including radiative accelerations of 28 species have been calculated for Pop II stars of 0.5 to 1.2 solar mass with [Fe/H] from -4.31 to -0.71. Overabundances are expected in some turnoff stars with effective temperatures larger than 5900 K. They depend strongly on the metallicity of the cluster. At the metallicity of M92 they reach a factor of 10 for many species at 12 Gyr but a factor of at most 2 at 13.5 Gyr. Series of models were also calculated with turbulence to determine to what extent turbulence reduces predicted abundance anomalies. The level of abundance anomalies observed in turnoff stars may then determine a level of turbulence. Even in the presence of turbulence however allowance for diffusive processes leads to a 10%-12% reduction in age at a given turnoff luminosity. For M 92 an age of 13.5 Gyr is determined which is about 1.5 Gyr younger than obtained in the absence of diffusion. In clusters atomic diffusion is now known to play a role in white dwarfs HB stars for age determination and for abundance anomalies in some turnoff stars.

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