Search Publications
Radiation-driven winds of hot luminous stars. XII. A first step towards detailed UV-line diagnostics of O-stars.
Butler, K.; Kudritzki, R. P.; Pauldrach, A. W. A. +2 more
Improved radiation driven wind models are constructed to calculate detailed synthetic UV spectra of hot luminous stars. The model improvements comprise: a very detailed multilevel non-local thermodynamic equilibrium (NLTE) treatment of 29 of the most important ionization stages, in particular C, N, O and Fe using accurate atomic data; the approxim…
Model atmospheres for Vega.
Castelli, F.; Kurucz, R. L.
We compared blanketed Local Thermodynamic Equilibrium (LTE) models for Vega computed both with the opacity distribution function (ODF) method and the opacity-sampling (OS) method. In the ODF case we used the ATLAS9 code with the new opacity data from Kurucz (1992). Model parameters for Vega depend on the amount of reddening and on the helium abund…
Is there primordial gas in IZw 18 ?
Kunth, D.; Sargent, W. L. W.; Lequeux, J. +1 more
The dwarf emission line galaxy IZw 18 has one of the lowest known O/H abundance ratios (O/H = 1.75 10^-5^) deduced from its emission lines. Its two main emission patches are associated with two extended HI clouds with very high column densities (N(HI) = 10^22^ H atoms cm^-2^). We have obtained spectra of the northwest emission region with the GHRS…
Temperatures and luminosities of symbiotic novae.
Murset, Urs; Nussbaumer, Harry
Symbiotic novae occur in double star systems, where mass lost by a red giant is accumulated by wind accretion onto a wite dwarf. When a critical mass has been reached, a nova-like outburst of long duration sets in, the outbursts lasts many dozons of years. We determine the evolution of luminosity and temperature during the outburst. We find slowly…
A study of the luminous blue variable candidate He 3-519 and its surrounding nebula.
Crowther, P. A.; Smith, L. J.; Prinja, R. K.
He 3-519 is 20 min away from the well-known Luminous Blue Variable (LBV) AG Car and is surrounded by a ring nebula 1 min diameter. In this paper, we present the first detailed study of He 3-519 and its surrounding nebula based on high resolution spectra obtained at the Anglo-Australian Telescope (AAT) with the University College London (UCL) echel…
Simultaneous observations of Seyfert 1 galaxies with IUE, ROSAT and GINGA
Walter, R.; Wamsteker, W.; Courvoisier, T. J. -L. +4 more
Simultaneous observations of 8 Seyfert 1 type active galactic nuclei (Fairall-9, Mrk 590, NGC 4051, 3C 273, NGC 5548, Mrk 841, Q1821+643 and 3C 390.3) obtained with IUE, ROSAT and, for 5 targets, with Ginga are presented and analysed with the aim to describe the ultraviolet to soft X-ray spectral component in these sources. The unobservable far ul…
Element abundances of classical novae.
Starrfield, S.; Drechsel, H.; Andrea, J.
Physical conditions and element abundances in the optically thin shells of 11 classical novae with outbursts between 1978 and 1989 were determined from an analysis of UV and optical spectra obtained during the nebular stage. Eight novae were studied on the basis of new optical and UV spectra: PW Vul (1984), QU Vul (1984), V842 Cen (1986), V827 Her…
Multi-wavelength monitoring of the BL Lacertae Object PKS 2155-304 II. The ROSAT Observations
Maraschi, L.; Treves, A.; Brinkmann, W. +7 more
Extensive ROSAT PSPC observations of the BL Lac object PKS 2155-304 carried out between November 12 and November 15, 1991 revealed the source to be in a bright state with a soft X-ray flux of F_x_(0.1-2.4keV)=~7x10^-10^erg/cm^2^/s. Rapid variations in the X-ray flux of up to 30% within a day were apparent but at the sampling rate of ~96 min all of…
Systematic study of the ultraviolet variability of active galactic nuclei.
Paltani, S.; Courvoisier, T. J. -L.
We have analysed all spectra of all active galactic nuclei (AGN) observed with the IUE satellite during the period 1978-1991. 90% of the 93 objects for which an estimate of the variability can be obtained have varied by more than 15% in the ultraviolet domain. In almost all objects the flux variations are more important at 1200 A (mean of 39%) tha…
FOS observations of G117-B15A and the blue edge of the ZZ Ceti instability strip.
Koester, D.; Vauclair, G.; Allard, N. F.
From an analysis of FOS observations of G117-B15A, one of the hottest members of the ZZ Ceti class, we derive an effective temperature of 12250+/-125K. Since several other DA near the blue edge of the instability strip must have very similar temperatures according to their UV spectra, it is likely that the blue edge is lower than assumed until now…