The Galactic metallicity gradient

We have previously published intermediate to hi,oh resolution spectroscopic observations of approximately 80 early B-type main-sequence stars situated in 19 Galactic open clusters/associations with Galactocentric distances di stributed over 6 less than or equal to R-g less than or equal to 18 kpc. Th is current study collates and re-analyses these equivalent-width datasets u sing LTE and non-LTE model atmosphere techniques, in order to determine the stellar atmospheric parameters and abundance estimates for C, N, O, Mg, Al and Si. The latter should be representative of the present-day Galactic in terstellar medium. Our extensive observational dataset permits the identifi cation of sub-samples of stars with similar atmospheric parameters and of h omogeneous subsets of lines. As such, this investigation represents the mos t extensive and systematic study of its kind to date. We conclude that the distribution of light elements (CI O, Mg & Si) in the Galactic disk can be represented by a linear, radial gradient of -0.07 +/- 0.01 dex kpc(-1) Our results for nitrogen and oxygen viz. (-0.09 +/- 0.01 d ex kpc(-1) and -0.067 +/- 0.008 dex kpc(-1)) are in excellent agreement wit h that found from the study of HII regions. We have also examined our datas ets for evidence of an abrupt discontinuity in the metallicity of the Galac tic disk near a Galactocentric distance of 10 kpc (see Twarog et al. 1997). However, there is no evidence to suggest that our data would be better fit ted with a two-zone model. Moreover, we observe a N/O gradient of -0.04 +/- 0.02 dex kpc(-1) which is consistent with that found for other spiral gala xies (Vila-Costas gr Edmunds 1993).