Oxygen and Neon Abundances of B-Type Stars in Comparison with the Sun

To revisit the long-standing problem of possible inconsistency concerning the oxygen composition in the current galactic gas and in the solar atmosphere (i.e., the former being appreciably lower by ~0.3 dex) apparently contradicting the galactic chemical evolution, we carried out oxygen abundance determinations for 64 mid- through late-B stars by using the O I 6156-8 lines while taking into account the non-LTE effect, and compared them with the solar O abundance established in the same manner. The resulting mean oxygen abundance was <A(O)> = 8.71 (+/- 0.06), which means that [O/H] (star-Sun differential abundance) is ~-0.1, the difference being less significant than previously thought. Moreover, since the 3D correction may further reduce the reference solar oxygen abundance (8.81) by ~0.1 dex, we conclude that the photospheric O abundances of these B stars are almost the same as that of the Sun. We also determined the non-LTE abundances of neon for the sample B stars from Ne I 6143/6163 lines to be <A(Ne)> = 8.02 (+/- 0.09), leading to the Ne-to-O ratio of ~0.2 consistent with the recent studies. This excludes a possibility of considerably high Ne/O ratio once proposed as a solution to the confronted solar model problem.
Comment: 11 pages, 7 figures, 2 tables, accepted for publication in PASJ, Vol.62, No.5 (2010)