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

Creators: Kirby, Evan N.; Fu, Xiaoting; Guhathakurta, Puragra

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 ⁷7Li(p, α)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.

Additional Information

The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank the editor and the anonymous referee for a timely and helpful report. Support for this work was provided by NASA through Hubble Fellowship grant 51256.01 awarded to E.N.K. by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. X.T.F. and P.G. acknowledge support by NSF grant AST 09-37525. X.T.F. and L.D. thank NSFC for support by grants Nos. 10973015 and 11061120454. PG acknowledges NSF grant AST-1010039. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facility: Keck:II (DEIMOS)

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