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

Abstract

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 helium-3. We present the evolution of [C/Fe], [N/Fe] and carbon-12/carbon-13 for three models: a carbon-normal metal-poor star, and two stars that have accreted material from a 1.5 solar mass AGB companion, one having received 0.01 solar masses of material and the other having received 0.1 solar masses. 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.

Accepted for publication in MNRAS. 7 pages, 8 figures

References in corpus (15)

• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• The Frequency of Carbon-Enhanced Metal-Poor Stars in the Galaxy from the HERES sample
• Rotational mixing in low-mass stars II. Self-consistent models of Pop II RGB stars
• First stars IX -Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios
• First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars
• Thermohaline mixing and gravitational settling in carbon-enhanced metal-poor stars
• Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants
• Carbon and Strontium Abundances of Metal-Poor Stars
• 3He-Driven Mixing in Low-Mass Red Giants: Convective Instability in Radiative and Adiabatic Limits
• Light element abundances in carbon-enhanced metal-poor stars
• Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study
• The Impact of Carbon Enhancement on Extra Mixing in Metal-Poor Stars
• Does simultaneous solution matter for stellar evolution codes?

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