期刊
ASTROPHYSICAL JOURNAL
卷 743, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/743/2/107
关键词
globular clusters: individual (M68, M3); stars: abundances; stars: late-type; stars: Population II
资金
- NSF of the USA [AST-0908326]
- W. M. Keck Foundation
- Gordon and Betty Moore Foundation
- Johns Hopkins University
- German Research Foundation (DFG) [SFB 881, A5]
- University of Massachusetts
- IPAC/Caltech
- NASA
- NSF
- Australian Astronomical Observatory
- Leibniz-Institut fur Astrophysik Potsdam (AIP)
- Australian National University
- Australian Research Council
- French National Research Agency
- German Research Foundation
- European Research Council [ERC-StG 240271]
- Istituto Nazionale di Astrofisica at Padova
- National Science Foundation of the USA [AST-0908326]
- Macquarie University
- Netherlands Research School for Astronomy
- Natural Sciences and Engineering Research Council of Canada
- Slovenian Research Agency
- Swiss National Science Foundation
- Science & Technology Facilities Council of the UK
- Opticon
- Strasbourg Observatory
- Universities of Groningen, Heidelberg, and Sydney
- STFC [ST/F002432/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/F002432/1, ST/H00243X/1] Funding Source: researchfish
- UK Space Agency [ST/I000852/1] Funding Source: researchfish
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0908326] Funding Source: National Science Foundation
We report the discovery of eight lithium-rich field giants found in a high-resolution spectroscopic sample of over 700 metal-poor stars ([Fe/H] < -0.5) selected from the Radial Velocity Experiment survey. The majority of the Li-rich giants in our sample are very metal-poor ([Fe/H] less than or similar to -1.9), and have a Li abundance (in the form of Li-7), A(Li) = log(n(Li)/n(H)) + 12, between 2.30 and 3.63, well above the typical upper red giant branch (RGB) limit, A(Li) < 0.5, while two stars, with A(Li) similar to 1.7-1.8, show similar lithium abundances to normal giants at the same gravity. We further included two metal-poor, Li-rich globular cluster giants in our sample, namely the previously discovered M3-IV101 and newly discovered (in this work) M68-A96. This comprises the largest sample of metal-poor Li-rich giants to date. We performed a detailed abundance analysis of all stars, finding that the majority of our sample stars have elemental abundances similar to that of Li-normal halo giants. Although the evolutionary phase of each Li-rich giant cannot be definitively determined, the Li-rich phase is likely connected to extra mixing at the RGB bump or early asymptotic giant branch that triggers cool bottom processing in which the bottom of the outer convective envelope is connected to the H-burning shell in the star. The surface of a star becomes Li-enhanced as Be-7 (which burns to Li-7) is transported to the stellar surface via the Cameron-Fowler mechanism. We discuss and discriminate among several models for the extra mixing that can cause Li production, given the detailed abundances of the Li-rich giants in our sample.
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