Abstract
The observations of carbon isotopic ratios in evolved stars suggest that nonstandard mixing is acting in low-mass stars as they are ascending the red giant branch. We propose a simple consistent mechanism, based on the most recent developments in the description of rotation-induced mixing reported by Zahn in 1992, which simultaneously accounts for the low 12C/13C ratios in globular cluster and field Population II giants and for the lithium abundances in metal-poor giant stars. It also leads to the destruction of 3He produced on the main sequence in low-mass stars. This should both naturally account for the recent measurements of 3He/H in Galactic H II regions and allow for high values of 3He observed in some planetary nebulae.
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