THE GALLIUM PROBLEM IN HGMN STARS

Previous studies of visible-region high-excitation lines of Ga II in H gMn stars have usually concluded that these lines (lambda lambda 4251- 4262 and lambda 6334) yield abundance estimates for gallium, similar t o 1 dex greater than the UV resonance lines. Of the explanations propo sed in the literature, we find that the presence of hyperfine structur e (hfs) in the lines is the most likely. We analyse Lick Hamilton Eche lle CCD spectra by spectrum synthesis with the code UCLSYN. Using the Bidelman & Corliss (1962) measurements of hfs in Ga 11, and the calcul ations given by Lanz et al. (1993), with the oscillator strengths by R yabchikova & Smirnov (1994), we determine a difference in abundance (v isual-UV) of only 0.2 dex. Of this difference, about 0.1 dex can be ex plained by the simplified approximation to the true hfs, which can be estimated theoretically, and the remaining 0.1 dex can probably be acc ounted for by the stratification of Ga found by Smith (1995, 1996b). W e conclude that the visible-region and UV abundances are in agreement within the errors of the determinations, and that the anomaly previous ly found by several investigations is an artifact of the simplified at omic line structures assumed, or results from the use of very differen t gf-values from those adopted here.