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The 6Li/7Li ratio in the metal-poor halo dwarfs HD 19445 and HD 84937

1993; IOP Publishing; Volume: 408; Linguagem: Inglês

10.1086/172585

1538-4357

Verne V. Smith, David L. Lambert, P. E. Nissen,

Geophysics and Gravity Measurements

view Abstract Citations (217) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The 6Li/ 7Li Ratio in the Metal-poor Halo Dwarfs HD 19445 and HD 84937 Smith, Verne V. ; Lambert, David L. ; Nissen, Poul E. Abstract High-resolution high SNR spectra of the Li I 6707 A line in the subdwarfs HD 19445 and HD 84937 have been analyzed for the presence of Li-6. By measurement of the Li I line's wavelength and analysis of its profile, the atmosphere of HD 84937 is shown to have a small amount of Li-6: R = Li-6/Li = 0.05 +/- 0.02. For HD 19445, an upper limit is set of R less than 0.02. The presence of Li-6 in HD 84937 is consistent with the mild depletion of Li-6 predicted by standard (nonrotating) models and the initial presence of Li-6 in the halo produced by (principally) alpha-on-alpha fusion reactions involving the cosmic rays that are required to account for the Be and B observed in subdwarfs. Depletion of Li-6 in the lower mass star HD 19445 is expected to remove the initial Li-6 content and, hence, the absence of Li-6 is expected. If Yale models of rotating subdwarfs are adopted, the predicted severe depletion of Li-6 and the observed survival of Li-6 in HD 84937 have to be reconciled. Four suggestions are made: the rotating models are inapplicable to halo dwarfs, production of Li-6 by cosmic rays has been underestimated, the required high initial Li-6 abundance of the halo was produced prior to the formation of the Galaxy, or the Li-6 was produced in stellar flares. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172585 Bibcode: 1993ApJ...408..262S Keywords: Abundance; Galactic Halos; Lithium Isotopes; Stellar Composition; Subdwarf Stars; Stellar Atmospheres; Stellar Spectra; Astrophysics; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; STARS: ABUNDANCES; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 19445; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 84937; STARS: POPULATION II full text sources ADS | data products SIMBAD (2)