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Evolution of the First Stars: CNO yields and the C-rich extremely metal poor stars

Published online by Cambridge University Press:  23 December 2005

Georges Meynet
Affiliation:
Geneva Observatory, CH–1290 Sauverny, Switzerland, email: georges.meynet@obs.unige.ch
Sylvia Ekström
Affiliation:
Geneva Observatory, CH–1290 Sauverny, Switzerland, email: georges.meynet@obs.unige.ch
André Maeder
Affiliation:
Geneva Observatory, CH–1290 Sauverny, Switzerland, email: georges.meynet@obs.unige.ch
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Abstract

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Rotating massive stars at $Z=10^{-8}$ and $10^{-5}$ lose a great part of their initial mass through stellar winds. The chemical composition of the rotationally enhanced winds of very low $Z$ stars is very peculiar. The winds show large CNO enhancements by factors of $10^3$ to $10^7$, together with large excesses of $^{13}$C and $^{17}$O and moderate amounts of Na and Al. The excesses of primary N are particularly striking. When these ejecta from the rotationally enhanced winds are diluted with the supernova ejecta from the corresponding CO cores, we find [C/Fe], [N/Fe],[O/Fe] abundance ratios very similar to those observed in the C–rich extremely metal poor stars (CEMP). We show that rotating AGB stars and rotating massive stars have about the same effects on the CNO enhancements. Abundances of s-process elements and the $^{12}$C/$^{13}$C ratio could help us to distinguish between contributions from AGB and massive stars. On the whole, we emphasize the dominant effects of rotation for the chemical yields of extremely metal poor stars.

Type
Contributed Papers
Copyright
© 2005 International Astronomical Union