Search Publications
EXOSAT observations of active galactic nuclei
McHardy, I.; Branduardi-Raymont, G.; Molteni, D. +3 more
EXOSAT observations of the Type 1 Seyfert galaxies NGC3783 and NGC5548 are reported. Contrary to previous findings, the X-ray spectrum of NGC3783 is not heavily cutoff at low energies. This suggest that the conditions of the broad-line region in NGC3783 are different from those in which the earlier data were obtained. We speculate on the presence …
Dwarf novae in outburst : simultaneous ultraviolet and optical observations of VW Hydri.
Verbunt, F.; Schwarzenberg-Czerny, A.; Ward, M. +4 more
The authors present simultaneous spectrophotometry of the dwarf nova VW Hydri in the range 1200 - 7000 Å. The main set of observations cover one complete outburst, including the rise and the decline. Comparing these data with data from other outbursts of VW Hyi it is found that all the data can be interleaved. This underlines the similarity in the…
Large Magellanic CLOUD-X-4 - 13.4 Pulsations and an X-Ray Flare Observed by EXOSAT
Pietsch, W.; Pakull, M.; Staubert, R. +1 more
EXOSAT observed LMC X-4 on November 17/19, 1983 for one 1.4 day binary period during the high state of the 30.5 day cycle. An eclipse with sharp ingress and slow egress was detected with an eclipse angle of 27.1±1.0 dgr. In the medium energy experiment the source showed a hard power law spectrum. Outside eclipse the source was remarkably constant …
Studies of hot B subdwarfs. III. Carbon, nitrogen and silicon abundances in three sdB stars.
Fontaine, G.; Sion, E. M.; Wesemael, F. +1 more
Optical and high-dispersion IUE observations of three hot B subdwarfs (UV 1758 + 36, Ton S-227, and Feige 65) are presented. These data are analyzed with model atmosphere techniques, and element abundances for C, N, and Si are derived. The abundances are either near (N) or below (C, Si) the solar value; large variations (1) in the extent of undera…
2AO526-328 - the White Dwarf Rotation Period Revealed
van Paradijs, J.; van der Klis, M.; King, A. R. +4 more
We report results from EXOSAT observations of the intermediate polar system 2A0526-328 (TV Col). The hard X-ray emission (2 8 keV) is modulated with a period of 1943 s, interpreted as the white-dwarf rotation period. Soft and hard X-ray emission show intensity minima, in phase with the orbital period of 0.2286 days; analysis of the hard X-ray spec…
Stratification of the Extended Atmosphere of the Wolf-Rayet Component of V444 Cygni
Cherepashchuk, A. M.; Eaton, J. A.; Khaliullin, Kh. F.
The authors have obtained ultraviolet spectra covering both eclipses of V444 Cyg. Striking atmospheric eclipses, of up to 0.7 mag in depth, were detected in individual strong lines as well as over large ranges of the continuum shortward of 1500 Å. The continuum in the 1560 - 1900 Å range is produced by electron scattering. At shorter wavelengths e…
He II lambda 1640/lambda 4686 and Lyalpha/Hβ ratios in the extraordinary Seyfert galaxy Markarian 359.
Davidson, K.; Gull, T. R.; MacAlpine, G. M. +1 more
The exceptionally narrow-lined Seyfert 1 galaxy Mrk 359 is ideally suited for determining reddening via the He II lambda 1640/lambda 4686 emission-line ratio. Here the validity of He II lines as a reddening indicator for quasars and Seyfert galaxies is reexamined and confirmed in the context of the most complete photoionization models available. I…
Magnetic Activity in Cool Stars
Schrijver, C. J.
Aspects of magnetic activity of late-type stars are reviewed: first, results obtained through the comparison of emissions from various temperature regimes in the outer atmospheres of cool stars, then results from stellar soft X-ray spectroscopy. Spectra obtained with different instruments (Imaging Proportional Counter and Solid State Spectrometer …
Two new color-selected magnetic DA white dwarfs.
Sion, E. M.; Green, R. F.; Boroson, T. A. +3 more
The discovery of two magnetic white dwarfs culled from blue star surveys is reported. The surveys were carried out with the Mount Lemnon 1.5-meter reflecting telescope attached to a two-holer polarimeter/photometer. Spectral observations of the objects, (PG 1533 - 057, and K813 - 14), indicate the presence of hydrogen and Zeeman components. On the…
Spectrum and Chemical Composition of the Remarkable Planetary Nebula NGC 6537
Czyzak, S. J.; Aller, Lawrence H.; Keyes, C. D. +1 more
Observations with the image tube scanner at the Shane 3-m telescope are combined with data obtained with the International Ultraviolet Explorer to assess the spectrum of the remarkable high-excitation planetary nebula NGC 6537. We have analyzed the spectrum of this nitrogen-rich object with the aid of the theoretical nebular models. The models per…