2014MNRAS.445..347K -
Mon. Not. R. Astron. Soc., 445, 347-358 (2014/November-3)
Helium enrichment and carbon-star production in metal-rich populations.
KARAKAS A.I.
Abstract (from CDS):
We present new theoretical stellar evolutionary models of metal-rich asymptotic giant branch (AGB) stars. Stellar models are evolved with initial masses between 1 and 7M☉ at Z = 0.007, and 1 and 8M☉ at Z = 0.014 (solar) and at Z = 0.03. We evolve models with a canonical helium abundance and with helium-enriched compositions (Y = 0.30, 0.35, and 0.40) at Z = 0.014 and 0.03. The efficiency of third dredge-up and the mass range of carbon stars decreases with an increase in metallicity. We predict carbon stars form from initial masses between 1.75 and 7M☉ at Z = 0.007 and between 2 and 4.5M☉ at solar metallicity. At Z = 0.03, the mass range for C-star production is narrowed to 3.25-4M☉. The third dredge-up is reduced when the helium content of the model increases owing to the reduced number of thermal pulses on the AGB. A small increase of ΔY = 0.05 is enough to prevent the formation of C stars at Z = 0.03, depending on the mass-loss rate, whereas at Z = 0.014, an increase of ΔY ≳ 0.1 is required to prevent the formation of C stars. We speculate that the probability of finding C stars in a stellar population depends as much on the helium abundance as on the metallicity. To explain the paucity of C stars in the inner region of M31, we conclude that the observed stars have Y ≳ 0.35 or that the stellar metallicity is higher than [Fe/H] ~ 0.1.
Abstract Copyright:
© 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society (2014)
Journal keyword(s):
stars: abundances - stars: AGB and post-AGB - stars: carbon - Galaxy: abundances - Galaxy: bulge - galaxies: abundances
Simbad objects:
10
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