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B stars and the chemical evolution of the Galactic disk *
T. Szeifert and
Received 15 May 1998 / Accepted 12 August 1998
We determine stellar parameters and He, C, N, O, Mg, Al, and Si abundances of a sample of 16 early B main-sequence stars in galactocentric distances of -14 kpc by reanalyzing and extending the observations of Kaufer et al. (1994) towards the Galactic center. The analysis uses Kurucz ATLAS 9 LTE atmospheres and Giddings-Butler DETAIL/SURFACE non-LTE line formation.
It is shown that beside non-LTE effects the metallicity of the underlying atmosphere has a non-negligible impact on the temperature structure and the subsequent line formation. The local field is found to have an underabundance of about relative to the Sun. Contrary to part of recent B-star and H II -region determinations we derive an oxygen abundance gradient [O/H] for the Galactic disk, typical for normal spiral galaxies of similar Hubble type.
This steep gradient is in contrast to the recent evidence that (a) our Milky Way is actually a barred spiral galaxy, and (b) barred galaxies generally have almost flat abundance gradients throughout their disks. Comparing our results with numerical models of the chemodynamical evolution of barred galaxies we derive an age of about 1 Gyr for the central bar structure of the Galaxy. We argue that our bar is still too young to exert a notable flattening effect on the chemical abundance gradient of the Galactic disk.
Key words: stars: abundances stars: early-type stars: fundamental parameters Galaxy: abundances Galaxy: evolution
Send offprint requests to: C.Gummersbach@lsw.uni-heidelberg.de
Online publication: September 17, 1998