2009MNRAS.396.1046L -
Mon. Not. R. Astron. Soc., 396, 1046-1057 (2009/June-3)
The evolution of low-metallicity asymptotic giant branch stars and the formation of carbon-enhanced metal-poor stars.
LAU H.H.B., STANCLIFFE R.J. and TOUT C.A.
Abstract (from CDS):
We investigate the behaviour of asymptotic giant branch (AGB) stars between metallicities Z = 10–4 and 10–8. We determine which stars undergo an episode of flash-driven mixing, where protons are ingested into the intershell convection zone, as they enter the thermally pulsing AGB phase and which undergo third dredge-up. We find that flash-driven mixing does not occur above a metallicity of Z = 10–5 for any mass of star and that stars above 2M☉ do not experience this phenomenon at any metallicity. We find carbon ingestion (CI), the mixing of carbon into the tail of hydrogen-burning region, occurs in the mass range 2M☉ to around 4M☉. We suggest that CI may be a weak version of the flash-driven mechanism. We also investigate the effects of convective overshooting on the behaviour of these objects. Our models struggle to explain the frequency of Carbon-Enhanced Metal-Poor (CEMP) stars that have both significant carbon and nitrogen enhancement. Carbon can be enhanced through flash-driven mixing, CI or just third dredge-up. Nitrogen can be enhanced through hot bottom burning and the occurrence of hot dredge-up also converts carbon into nitrogen. The C/N ratio may be a good indicator of the mass of the primary AGB stars.
Abstract Copyright:
© 2009 The Authors. Journal compilation © 2009 RAS
Journal keyword(s):
stars: AGB and post-AGB - stars: carbon - stars: evolution
CDS comments:
In Chap. 5 : HE 1317-2326 is a misprint for HE 1327-2326
Simbad objects:
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