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Astron. Astrophys. 352, L40-L44 (1999)

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Letter to the Editor

VLT FORS spectra of blue supergiants in the Local Group galaxy NGC 6822

B. Muschielok 1, R.P. Kudritzki 1,2,3, I. Appenzeller 6, F. Bresolin 5, K. Butler 1, W. Gässler 1, R. Häfner 1, H.J. Hess 1, W. Hummel 1, D.J. Lennon 4, K.-H. Mantel 1, W. Meisl 1, W. Seifert 6, S.J. Smartt 4, T. Szeifert 6 and K. Tarantik 1

1 Institut für Physik und Astronomie, Scheinerstrasse 1, 81679 München, Germany
2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85740 Garching bei München, Germany
3 University of Arizona, Steward Observatory, 933 N. Cherry Av., Tucson, AZ 85721, USA
4 Isaac Newton Group of Telescopes, Apartado de Correos 368, 38700 Santa Cruz de la Palma, Spain
5 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
6 Landessternwarte Heidelberg, Königstuhl, 69117, Heidelberg, Germany

Received 16 August 1999 / Accepted 2 September 1999

Abstract

Half hour exposures using the ESO VLT/FORS1 combination at Parañal in Chile have allowed us to obtain spectra for three B supergiants in the dwarf irregular galaxy NGC 6822. The spectra have been analysed using non-LTE techniques and temperatures, gravities, helium content and abundances have been obtained. Overall the metallicity of NGC 6822 is found to lie between that of the LMC and of the SMC, in agreement with previous observations of H II regions and in contrast to the earlier findings of Massey et al. (1995). The analysis of [FORMULA] yields estimates of the mass-loss rates and wind momenta. These results demonstrate that significantly longer exposures with the same instruments will allow us to perform quantitative spectroscopy of blue supergiants in galaxies far beyond the Local Group.

Key words: atomic data – line: formation – stars: Hertzsprung – Russel (HR) and C-M diagrams – stars: early-type – stars: supergiants

Send offprint requests to: K.Butler

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© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999
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