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Astron. Astrophys. 333, 665-672 (1998)

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The gallium problem in HgMn stars

M.M. Dworetsky *, C.M. Jomaron and Claire A. Smith

Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Received 19 September 1997 / Accepted 15 January 1998

Abstract

Previous studies of visible-region high-excitation lines of Ga ii in HgMn stars have usually concluded that these lines ([FORMULA] 4251-4262 and [FORMULA] 6334) yield abundance estimates for gallium [FORMULA] 1 dex greater than the UV resonance lines. Of the explanations proposed in the literature, we find that the presence of hyperfine structure (hfs) in the lines is the most likely. We analyse Lick Hamilton Échelle CCD spectra by spectrum synthesis with the code UCLSYN. Using the Bidelman & Corliss (1962) measurements of hfs in Ga ii, and the calculations given by Lanz et al. (1993), with the oscillator strengths by Ryabchikova & Smirnov (1994), we determine a difference in abundance (visual-UV) of only 0.2 dex. Of this difference, about 0.1 dex can be explained by the simplified approximation to the true hfs, which can be estimated theoretically, and the remaining 0.1 dex can probably be accounted for by the stratification of Ga found by Smith (1995, 1996b). We conclude that the visible-region and UV abundances are in agreement within the errors of the determinations, and that the anomaly previously found by several investigations is an artifact of the simplified atomic line structures assumed, or results from the use of very different gf -values from those adopted here.

Key words: stars: abundances – stars: chemically peculiar – stars: rotation – atomic data

* Guest Observer, Lick Observatory

Send offprint requests to: M.M. Dworetsky (mmd@star.ucl.ac.uk)

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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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