The Abundance of Gallium in B-Type Chemically Peculiar Stars

Abstract

Quantitative analyses of the Ga abundances in 27 Hg-Mn stars, 11 Si (magnetic) stars, eight He-weak stars, and seven normal stars are made with the resonance lines of Ga II at 1414 A and Ga III at 1495 A in International Ultraviolet Explorer (IUE) spectra. The Ga overabundances are confirmed as a genuine anomaly in many peculiar stars. Only upper limits of the Ga abundance can be obtained for some stars. However, these upper limits are much lower than those inferred from visual spectra. Among the 27 Hg-Mn stars, 17 stars are distributed in a range of 2.0-3.8 dex of overabundances of Ga. Ten other stars show upper limits of less than 2.1 dex. Fifteen of the 20 hotter Hg-Mn stars, with Teff greater than 11,000 K, show high overabundances in a narrow range of 2.6-3.8 dex, while among seven cooler Hg-Mn stars, only the star HR 7775 shows the same overabundance as in the hotter 15 stars. Of 11 Si stars, nine stars have Ga overabundances ranging from 1.9 to 3.2 dex. Gallium is overabundant in five out of eight He-weak stars in the range of 1.7-3.2 dex, while in the three other stars the upper limits are less than 1.3 dex. The Ga abundances in normal stars are all upper limits which roughly correspond to the solar value.