Discovery of Super-Li Rich Red Giants in Dwarf Spheroidal Galaxies

TL;DR

This study identifies 15 lithium-rich red giants in dwarf spheroidal galaxies, including the most metal-poor Li-enhanced star, suggesting lithium enrichment may be a brief, universal phase in stellar evolution.

Contribution

The paper reports the discovery of 15 Li-rich red giants in dwarf galaxies, doubling known low-mass, metal-poor Li-rich giants and highlighting potential universal lithium enrichment in stellar evolution.

Findings

15 Li-rich red giants identified, including the most metal-poor star known.

Most Li-rich stars have lithium levels exceeding primordial values.

Li enrichment may be a brief, universal evolutionary phase.

Abstract

Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of K, hot enough for the 7Li(p,alpha)4He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants--14 of which are new discoveries--among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] <~ -0.7) Li-rich red giants, and it includes the most-metal poor Li-enhanced star known ([Fe/H] = -2.82, A(Li)_NLTE = 3.15). Because most of these stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and it seems rare only because it is brief.