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Astron. Astrophys. 353, 311-321 (2000)

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An exploratory non-LTE analysis of B-type supergiants in the Small Magellanic Cloud

P.L. Dufton  *  1, N.D. McErlean 1, D.J. Lennon 2 and R.S.I. Ryans 1

1 The Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, Ireland
2 Isaac Newton Group of Telescopes, Apartado de Correos 368, 38700 Santa Cruz de La Palma, Canary Islands, Spain

Received 2 July 1999 / Accepted 8 October 1999


A preliminary differential non-LTE model atmosphere analysis of moderate resolution ([FORMULA] 5 000) and signal-to-noise ratio spectra of 48 Small Magellanic Cloud B-type supergiants is presented. Standard techniques are adopted, viz. plane-parallel geometry and radiative and hydrostatic equilibrium. Spectroscopic atmospheric parameters ([FORMULA], [FORMULA] and [FORMULA]), luminosities and chemical abundances (He, C, N, O, Mg and Si) are estimated.

These are compared with those deduced for a comparable sample of Galactic supergiants. The SMC targets appear to have similar atmospheric parameters, luminosities and helium abundances to the Galactic sample. Their magnesium and silicon underabundances are compatible with those found for main sequence SMC objects and there is no evidence for any large variation in their oxygen abundances. By contrast both their carbon and nitrogen lines strengths are inconsistent with single abundances, while their nitrogen to carbon abundance ratios appear to vary by at least as much and probably more than that found in the Galactic sample.

Key words: stars: atmospheres – stars: early-type – stars: evolution – stars: supergiants – galaxies: abundances – galaxies: Magellanic Clouds

* On leave of absence at the Isaac Newton Group of Telescopes, Apartado de Correos 368, E-38700, Santa Cruz de La Palma, Canary Islands, Spain

Send offprint requests to: P.L. Dufton (P.Dufton@qub.ac.uk)

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© European Southern Observatory (ESO) 2000

Online publication: December 8, 1999