Lithium 6104 Å in Population II stars

Free access article

Issue		A&A Volume 393, Number 2, October II 2002


Page(s)		617 - 628
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20021040

A&A 393, 617-628 (2002)
DOI: 10.1051/0004-6361:20021040

Lithium 6104 Å in Population II stars

A. Ford^{1, 2}, R. D. Jeffries¹, B. Smalley¹, S. G. Ryan², W. Aoki³, S. Kawanomoto³, D. J. James^{4, 5, 6} and J. R. Barnes⁴

¹ Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG, UK
    e-mail: alison.ford@open.ac.uk; rdj@astro.keele.ac.uk; bs@astro.keele.ac.uk
² Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
    e-mail: s.g.ryan@open.ac.uk
³ National Astronomical Observatory of Japan, Mitaka, Tokyo, 181-8588 Japan
    e-mail: aoki.wako@noa.ac.jp; kawanomo@optik.mtk.nao.ac.jp
⁴ School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9SS, UK
⁵ Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble, Cedex 9, France
    e-mail: djames@obs.ujf-grenoble.fr
⁶ Observatoire de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland

(Received 23 January 2002 / Accepted 11 July 2002)

Abstract
We have obtained échelle spectroscopy of 14 Population II objects selected from those previously observed by Bonifacio & Molaro (1997). For one object, HD 140283, we obtained exquisite data with the High Dispersion Spectrograph on the Subaru Telescope, with S/N exceeding 1000 per 0.018 Å pixel. Li abundances have been determined by spectral synthesis from both the 6708 Å resonance line and also from 6104 Å subordinate feature. Firm detections of the weak line have been made in seven objects, and upper limits are reported for the remainder. Our 6708 Å abundances agree with those reported by Bonifacio & Molaro with a mean difference of only 0.019 $\pm$ 0.009 dex. Abundances from the 6104 Å line hint at a higher Li abundance than that determined from the resonance feature, but this evidence is mixed; the weakness of the 6104 Å line and the large number of upper limits make it difficult to draw firm conclusions. NLTE-corrections increase (rather than eliminate) the size of the (potential) discrepancy, and binarity appears unlikely to affect any abundance difference. The effect of multi-dimensional atmospheres on the line abundances was also considered, although it appears that use of 3-D (LTE) models could again act to increase the discrepancy, if one is indeed present.

Key words: stars: abundances -- stars: Population II -- stars: interiors

Offprint request: A. Ford, alison.ford@open.ac.uk

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