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The Role of Technetium in the Evolution of Red Giants

Published online by Cambridge University Press:  12 April 2016

Irene R. Little-Marenin
Irene R. Little-Marenin*
Affiliation:
Wellesley College, Wellesley, MA, USA 02181

Abstract

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Tc is detected in many AGB stars providing unambiguous proof that recent nuclear s-processing and mixing (the third dredge-up) has taken place. During this evolutionary episode the atmospheres of AGB stars are progressively enhanced with helium burning products (primari ly l2C) and s-process elements as they evolve from M->MS->S->SC->C stars. The increase in s-process elements can be traced most easily by the presence and increasing strength of the Tc I lines accompanying this progression. We also find that the third dredge-up phase is accompanied by an increase in the amplitude of light variation since no non-variable or low amplitude variable M, MS, SC, or S (with one exception) have Tc lines. M star Mira variables show Tc if P > 300d (low mass Pop I stars). No Pop II star is known to have Tc. Nor do supergiants show Tc I lines. The significant fraction of MS, S and C stars that do not show Tc, are surmised to be cooler analogues to the Ba II stars, i.e. binaries. The source to provide the neutrons for the s-process is most likely the 13C(a, n)16O reaction since most of the stars in which we observe Tc are thought to have masses less than 3 solar masses.

Type
2. Model Photospheres and Chemical Compositions
Information
International Astronomical Union Colloquium , Volume 106: Evolution of Peculiar Red Giant Stars , 1989 , pp. 131 - 143
Copyright
Copyright © Cambridge University Press 1989

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