DISCOVERY OF SUPER-Li-RICH RED GIANTS IN DWARF SPHEROIDAL GALAXIES

Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of kelvin, hot enough for the Li-7(p, alpha)He-4 reaction to burn Li efficiently. Only about 1% of first-ascent red giantsmore 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] less than or similar to -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 the 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.