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Astron. Astrophys. 333, 665-672 (1998)
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]](img1.gif)
4251-4262 and ![[FORMULA]](img2.gif)
6334) yield
abundance estimates for gallium ![[FORMULA]](img3.gif)
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)
Contents
- 1. Introduction
- 2. Observations
- 3. Atomic data
- 4. Abundance analysis for Ga II
- 4.1. Individual lines
- 4.2. Equivalent widths
- 5. Discussion
- 6. Conclusions
- Acknowledgements
- References
© European Southern Observatory (ESO) 1998
Online publication: April 20, 1998
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