The depletion of carbon by extra mixing in metal-poor giants

Summary, in English

There is an apparent dichotomy between the metal-poor ([Fe/H] ≤ -2) yet carbon-normal giants and their carbon-rich counterparts. The former undergo significant depletion of carbon on the red giant branch after they have undergone first dredge-up, whereas the latter do not appear to experience significant depletion. We investigate this in the context that the extra mixing occurs via the thermohaline instability that arises due to the burning of ³He. We present the evolution of [C/Fe], [N/Fe] and ¹²C/¹³C for three models: a carbon-normal metal-poor star, and two stars that have accreted material from a 1.5 M_⊙ AGB companion, one having received 0.01 M_⊙ of material and the other having received 0.1 M_⊙. We find the behaviour of the carbon-normal metal-poor stars is well reproduced by this mechanism. In addition, our models also show that the efficiency of carbon-depletion is significantly reduced in carbon-rich stars. This extra-mixing mechanism is able to reproduce the observed properties of both carbon-normal and carbon-rich stars.

• Author: Richard J. Stancliffe; Ross P. Church; George C. Angelou; John C. Lattanzio
• Publishing year: 2009-07-01
• Language: English
• Pages: 2313-2318
• Publication/Series: Monthly Notices of the Royal Astronomical Society
• Volume: 396
• Issue: 4
• Links: http://dx.doi.org/10.1111/j.1365-2966.2009.14900.x
• Document type: Journal article
• Publisher: Oxford University Press
• Topic: Astronomy, Astrophysics and Cosmology
• Keywords: Stars: AGB and post-AGB; Stars: carbon; Stars: evolution; Stars: Population II
• Status: Published
• ISBN/ISSN/Other: ISSN: 0035-8711