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Astron. Astrophys. 363, 537-554 (2000)

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The Galactic metallicity gradient

W.R.J. Rolleston 1, S.J. Smartt 2,3, P.L. Dufton *  1 and R.S.I. Ryans 1

1 Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, N. Ireland, UK (R.Rolleston@qub.ac.uk)
2 The Isaac Newton Group of Telescopes, Apartado de Correos 368, 38780 Santa Cruz de La Palma, Canary Islands, Spain
3 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, England, UK

Received 16 February 2000 / Accepted 11 September 2000

Abstract

We have previously published intermediate to high resolution spectroscopic observations of approximately 80 early B-type main-sequence stars situated in 19 Galactic open clusters/associations with Galactocentric distances distributed over [FORMULA] kpc. This current study collates and re-analyses these equivalent-width datasets using 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 interstellar medium. Our extensive observational dataset permits the identification of sub-samples of stars with similar atmospheric parameters and of homogeneous subsets of lines. As such, this investigation represents the most extensive and systematic study of its kind to date.

We conclude that the distribution of light elements (C, O, Mg & Si) in the Galactic disk can be represented by a linear, radial gradient of [FORMULA] dex kpc-1. Our results for nitrogen and oxygen viz. [FORMULA] dex kpc-1 and [FORMULA] dex kpc[FORMULA] are in excellent agreement with that found from the study of H II regions. We have also examined our datasets for evidence of an abrupt discontinuity in the metallicity of the Galactic 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 fitted with a two-zone model. Moreover, we observe a N/O gradient of [FORMULA] dex kpc-1 which is consistent with that found for other spiral galaxies (Vila-Costas & Edmunds 1993).

Key words: stars: abundances – stars: early-type – Galaxy: abundances – Galaxy: evolution

* Visiting Astronomer, ING Telescopes, La Palma

Send offprint requests to: W.R.J. Rolleston

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© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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