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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…
Optical spectroscopy and photometry of the periodic X-ray transient AO 538-66 ( X 0535-668) during an outburst and an OFF state.
Parmar, A. N.; Branduardi-Raymont, G.; Mason, K. O. +2 more
Optical spectroscopy and photometry of the periodic X-ray transient A0538 - 66 are presented. Extensive spectroscopy performed in March 1982 follows the evolution of the multi-component line profiles through an outburst. Particularly distinctive are the broad, asymmetric emission lines which are interpreted as arising in an extensive stellar wind.…
The ultraviolet spectrum of the Be star HD 50138.
Hutsemekers, D.
The ultraviolet spectrum of the B8 Ve star HD 50138, recorded during the December 1978-January 1982 period with IUE, is analyzed. The spectrum is found to be crowded by absorption lines, mostly those of singly ionized iron peak elements. In addition there are broad lines essentially due to superionized species (Si IV, C IV) and a P Cygni profile f…
Line identifications, line strengths and continuum flux measurements in the ultraviolet spectrum of Arcturus.
Carpenter, K. G.; Stencel, R. E.; Wing, R. F.
The ultraviolet spectrum of Arcturus has been observed at high resolution with the IUE satellite. Line identifications, mean absolute 'continuum' flux measurements, integrated absolute emission-line fluxes, and measurements of selected absorption line strengths are presented for the 2250-2930 A region. In the 1150-2000 A region, identifications ar…
Carbon IV absorption troughs in the ultraviolet spectra of Be stars :gone with the wind ?
Marlborough, J. M.; Barker, P. K.
IUE observations of five Be stars reveal striking and previously unrecognized forms of stellar wind variability. Broad C IV double-lambda 1548,1550 absorption troughs, which underlie shortward-shifted narrow absorption components, may disappear or reappear. The C IV equivalent width can vary by a factor approximately equal to or greater than 5 on …