Episodic lithium production by extra-mixing in red giants

Abstract

The recent discovery of low-mass red giants with enhanced atmospherical Li abundance in galactic low-metallicity stellar clusters adds to the mysterious phenomenon of the Li-rich giants. We propose a combined scenario for the Li-enrichment: engulfing a giant planet (or brown dwarf) by a red giant (external source) activates inside the giant the "7Be-mechanism" producing Li internally. This episodical Li-production can happen at any time on the red giant branch and is naturally followed by Li-depletion as is observed. Limitations of our scenario are discussed as well.