Search Publications
HST study of Lyman-alpha emission in star-forming galaxies: the effect of neutral gas flows
Mas-Hesse, J. M.; Terlevich, E.; Terlevich, R. +3 more
We present high dispersion HST GHRS UV spectroscopic observations of 8 H II galaxies covering a wide range of metallicities and physical properties. We have found Lyalpha \ emission in 4 galaxies with blueshifted absorption features, leading to P Cygni like profiles in 3 of them. In all these objects the O I and Si II absorption lines are also blu…
An ultraviolet, optical and infrared study of Herbig Ae/Be stars
Waelkens, C.; Malfait, K.; Bogaert, E.
We have selected a list of 45 Herbig Ae/Be-type candidates on the base of their IRAS colors and their spectral types. We propose the presence of a broad infrared excess as a defining criterion for these stars, rather than the detection of circumstellar nebulosity. In this way, our selection also includes more evolved young stars, that are no longe…
Spectral analyses of PG 1159 star: constraints on the GW Virginis pulsations from HST observations
Dreizler, S.; Heber, U.
We present the results of a quantitative analysis of UV and optical spectra of nine PG 0122+200ls, very hot hydrogen-deficient [pre-] white dwarfs, by means of line blanketed NLTE model atmospheres. Four programme stars constitute the GW Vir variables, a class of non-radial g-mode pulsators. Precise effective temperatures, carbon, nitrogen and oxy…
The nitrogen spectra of Wolf-Rayet stars. A grid of models and its application to the Galactic WN sample
Hamann, W. -R.; Koesterke, L.
Adopting the ``standard model'' for Wolf-Rayet atmospheres, non-LTE radiation transfer calculations are performed which account for helium and nitrogen. Grids of theoretical models are presented for the whole relevant parameter range. The WN classification criteria are employed in order to identify the subtype domains, and inconsistencies are disc…
An analysis of DA white dwarfs from the Hamburg Quasar Survey
Reimers, D.; Dreizler, S.; Heber, U. +5 more
Follow-up spectroscopy of several hundred hot stars detected by the Hamburg Quasar Survey (HQS) has been carried out between 1989 and 1996. We present the analysis of 80 DA white dwarfs using model atmospheres and theoretical cooling tracks to derive the atmospheric parameters T_eff and log g, masses and absolute magnitudes. The HQS turned out to …
HST/GHRS observations of AM Herculis
Gänsicke, B. T.; Beuermann, K.; Szkody, P. +2 more
We present phase-resolved spectroscopy of AM Herculis obtained with the HST/GHRS when the system was in a high state. The ultraviolet light curve shows a quasi-sinusoidal modulation, which can be explained by a hot spot on the rotating white dwarf. The broad Lyalpha absorption expected for photospheric radiation of a moderately hot white dwarf is …
The HIPPARCOS Hertzsprung-Russell diagram of S stars: probing nucleosynthesis and dredge-up
Jorissen, A.; Udry, S.; Mayor, M. +2 more
HIPPARCOS trigonometrical parallaxes make it possible to compare the location of Tc-rich and Tc-poor S stars in the Hertzsprung-Russell (HR) diagram: Tc-rich S stars are found to be cooler and intrinsically brighter than Tc-poor S stars. The comparison with the Geneva evolutionary tracks reveals that the line marking the onset of thermal pulses on…
Quantitative UV spectroscopy of early O stars in the Magellanic Clouds. The determination of the stellar metallicities
Lennon, D. J.; Pauldrach, A. W. A.; Puls, J. +4 more
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 T_eff,log g, R_{*}, and the mass loss rates dot {M} known from optical analyses, the metal abundances including iron group elements are derived in two steps…
The blue-bump of 3C 273
Paltani, S.; Walter, R.; Courvoisier, T. J. -L.
We present optical and ultraviolet observations of 3C 273 covering the whole life of the IUE satellite. We analyze the variability properties of the light curves, and find that two variable components, written V_\nuAA\ and S_\nuBB\ respectively, must contribute to the S_\nuB\ emission in this object. The V_\nuAA\ component produces most of the var…
Spectral analysis of O(He)-type post-AGB stars
Rauch, T.; Dreizler, S.; Wolff, B.
We present an analysis of two recently discovered, very hot hydrogen-deficient post-AGB stars of spectral type O(He), namely HS 1522+6615 and HS 2209+8229, by means of state-of-the-art NLTE model atmospheres based on new optical, UV, and X-ray observations. In the spectra of HS 1522+6615 we discovered a variability of the \Ionw{O}{6}{5290} line co…