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Chemical Compositions of Population II Mid- and Late-Type Stars
Published online by Cambridge University Press: 19 July 2016
Abstract
The abundance patterns in Population II red giants provide information about galactic chemical evolution and nucleosynthesis sites for various chemical elements. These patterns were first revealed by moderate-S/N photographic spectra and are now being refined and extended to additional chemical elements and fainter stars with high-S/N data. The well-established features include overabundances of O and Ca, underabundances of s-process elements, and solar ratios of heavy r-process elements. An excess of nickel found by us on moderate-S/N spectra is less certain, and should be checked with high-S/N data. New information on oxygen abundances in Population II red giants is becoming available from high-S/N observations of weak [O I] lines, and consistently indicates an oxygen overabundance due to the preferential sampling in Population II stars of ejecta from massive stars of previous generations. Recent studies of highly evolved, post-AGB Population II stars are revealing remarkable overabundances of light elements (C, N, O, and S) and deficiencies of the heaviest elements; these are probably signatures of internal nucleosynthesis followed by mixing up to, or exposure by mass loss at, the stellar surface.
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- VI. Chemical Composition of Stars
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- Copyright © Kluwer 1988