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Abteilung Astronomie

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Preprint 02b/98

Analysis of IUE spectra of hot compact stars with NLTE model atmospheres

T. Rauch

Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

in Ultraviolet Astrophysics Beyond the IUE Final Archive, November 11-14, 1997, Sevilla, Spain, (Eds. R.González-Riestra, W. Wamsteker, R.A. Harris), ESA Publication Division, ESA-SP 413

Abstract. The flux maximum of hot stars is located in the UV/EUV wavelength range, hence they are fainter in the optical and, moreover, their optical spectra appear comparably poor in spectral features, displaying only lines of one ionization stage per element in many cases. Thus, high resolution and high signal-to-noise UV spectra are essential for a precise spectral analysis of these stars because many diagnostic lines can be identified in the UV. IUE had opened this spectral window - at a time when no metal-line blanketed NLTE model atmosphere was available for an adequate analysis of the overwhelming spectral information.

Taking up the challenge of improved observation, spectral analysis by means of NLTE model atmosphere techniques has steadily been developed within the lifetime of IUE. Other satellites like EUVE have opened new windows to the higher energy regions in which many metal lines can be found which are also very useful for photospheric diagnostics.

Presently available NLTE model atmospheres provide realistic fluxes for the analysis of the complete (IR to X-ray) wavelength range of hot compact stars.

Key words: non-LTE; stellar atmospheres; ultraviolet: stars

Paper (128k gzip'ed Postscript including figures)

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