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Astron. Astrophys. 330, 285-305 (1998)


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Quantitative UV spectroscopy of early O stars
in the Magellanic Clouds *

The determination of the stellar metallicities

S.M. Haser 1, A.W.A. Pauldrach 1, D.J. Lennon 1, R.-P. Kudritzki 1, 2, M. Lennon 1, 2, J. Puls 1 and S.A. Voels 3

1 Universitäts-Sternwarte München, Scheinerstr. 1, D-81679 München, Germany
2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching bei München, Germany
3 Astrophysics Data Facility, Code 631, Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

Received 5 June 1997 / Accepted 29 September 1997

Abstract

UV spectra of 4 O-stars in the Magellanic Clouds obtained with the Faint Object Spectrograph of the Hubble Space Telescope are analyzed with respect to metallicity. With the stellar parameters [FORMULA], [FORMULA], and the mass loss rates [FORMULA] known from optical analyses, the metal abundances including iron group elements are derived in two steps. First, hydrodynamic radiation driven wind NLTE models with metallicity as a free parameter are constructed to fit the observed wind momentum rate and thus, yield a dynamical metallicity. Then, synthetic spectra are computed for different metal abundances and compared to the observed spectra to obtain a spectroscopic metallicity. In general, the results obtained from both methods agree.

For the two stars in the Small Magellanic Cloud (NGC 346#3, O3 III(f [FORMULA]) and AV 243, O6 V) metallicities of [FORMULA] and -0.8, respectively, are found. The O3 star shows evidence for CNO-cycled matter in its atmosphere. The metallicity of the two stars in the Large Cloud (Sk [FORMULA], O3 III(f [FORMULA]) and Sk [FORMULA], O4 If [FORMULA]) are constrained to [FORMULA] and -0.1. Because of saturation effects in the cores of the pseudophotospheric metal lines the determination of the LMC metallicity is less reliable.

Key words: stars: early type; mass loss – line: profiles – stars: abundances – Magellanic Clouds

* Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Send offprint requests to: R.P. Kudritzki

© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998
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