Search Publications
O-star mass-loss and wind momentum rates in the Galaxy and the Magellanic Clouds Observations and theoretical predictions.
Lennon, D. J.; Herrero, A.; Pauldrach, A. W. A. +8 more
A new, very fast approximate method is presented to determine mass-loss rates of O-stars from Halpha_ line profiles. The method uses H and HeII departure coefficients from unified model atmospheres parametrized in a simple way as function of wind velocity together with photospheric NLTE line profiles as the inner boundary condition for …
X-ray properties of active galactic nuclei with optical FeII emission.
Wang, T.; Brinkmann, W.; Bergeron, J.
ROSAT spectra of 86 Active Galactic Nuclei (AGN) with a broad range of optical FeII strengths have been analyzed. The results of the spectral analysis have been combined with optical and radio data as well as with optical emission line properties collected from the literature to understand the origin of the strong FeII emission and the nature of t…
Spectral analysis of hot helium-rich white dwarfs.
Werner, K.; Dreizler, S.
We present a model atmosphere analysis of most known hot helium-rich white dwarfs of spectral type DO. The stars represent the non-DA white dwarf cooling sequence from the hot end (T_eff_=~120000K) down to the DB gap (T_eff_=~45000K). From medium resolution optical spectra, effective temperatures, surface gravities, and element abundances are dete…
Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.
Stahl, O.; Wolf, B.; Kaufer, A. +5 more
We have obtained time series of spectra in the wavelength range 4000-6800 A over several months with high S/N and high resolution in wavelength (λ/{DELTA}λ=~20000) and time ({DELTA}t=~1d) of the late-type B and early-type A supergiants HD91619 (B7Ia), βOri (B8Ia), HD96919 (B9Ia), HD92207 (A0Ia), HD100262 (A2Ia) and αCyg (A2Ia). Halpha_ …
Spectral analyses of late-type WC central stars of planetary nebulae.
Hamann, W. -R.; Jeffery, C. S.; Leuenhagen, U.
The optical spectra of the seven late-type Wolf-Rayet central stars NGC40 ([WC8]), BD+30 3639 ([WC9]), He2-99 ([WC9]), CPD-56 8032, He2-113, M4-18 and K2-16 (all [WC11]) are analyzed by means of spherically expanding model atmospheres. The NLTE simulations account for the elements helium, carbon and oxygen. As main results effective temperature T_…
Phase-locked photospheric and stellar-wind variations of θ^1^Orionis C.
Stahl, O.; Wolf, B.; Pakull, M. W. +9 more
We have obtained a long series of optical spectra and new IUE spectra of θ^1^Ori C, the brightest star in the Orion Trapezium and the main source of ionization of the Orion nebula (M 42). With these data, we have improved the accuracy of the period of the optical emission-line variations and the UV stellar-wind absorption-line variations. We find …
The X-ray source in non-magnetic cataclysmic variables.
Beuermann, K.; Verbunt, F.; van Teeseling, A.
We have analysed all available rosat pspc observations of non-magnetic cataclysmic variables. The VY Scl and non-SU UMa systems have harder X-ray spectra than the SU UMa and UX UMa systems. The old nova RR Pic has a very soft X-ray spectrum and might not be an ordinary non-magnetic cataclysmic variable. There appears to be no clear correlation of …
Discovery of four white dwarfs with strong magnetic fields by the Hamburg/ESO Survey.
Reimers, D.; Jordan, S.; Bade, N. +3 more
Four magnetic white dwarfs have been found in the course of the Hamburg/ESO Survey for bright QSOs. The objects have been selected as QSO candidate on the basis of its blue continuum and the apparent absence of strong hydrogen or helium lines. One star, HE1211-1707, shows a rather fast spectral variability: both the strength and the position of th…
The behaviour of the excess CA II H and K and Hɛ emissions in chromospherically active binaries.
Montes, D.; Fernandez-Figueroa, M. J.; de Castro, E. +1 more
In this work we analyze the behaviour of the excess Ca II H and K and Hɛ emissions in a sample of 73 chromospherically active binary systems (RS CVn and BY Dra classes), of different activity levels and luminosity classes. This sample includes the 53 stars analyzed by Fernandez-Figueroa et al. (1994) and the observations of 28 systems described by…
The cooling of the white dwarf in VW Hyi.
Gänsicke, B. T.; Beuermann, K.
We present an analysis of the post-outburst evolution of VW Hyi based on the available IUE archive data. The spectrum closest to the previous outburst (~0.5days) shows a non-negligible contribution of a disc remnant while the white dwarf (WD) dominates the later observations. Following an outburst, the accretion-heated WD cools exponentially to a …