Search Publications
The X-Ray Absorption Spectrum of VELA X-1
Haberl, F.; White, N. E.
Exosat observations of the massive X-ray binary Vela X-1 are spectrally analyzed. The absorbing column density shows erratic factor of 10 increases up to 5 x 10 to the 23rd H/sq cm that can occur at any orbital phase and last from minutes to many hours. These variations occur on top of a base level of absorption that increases from 3 x 10 to the 2…
The Discovery of Magnetically Controlled Circumstellar Matter in the Helium-weak Stars HD 5737 and HD 79158
Shore, Steven N.; Brown, Douglas N.; Sonneborn, George +2 more
The paper reports the discovery, using combined IUE spectroscopy and Zeeman polarimetric magnetic field measurements, of magnetically controlled circumstellar material in two helium-weak stars. HD 5737 = Alpha Sculptoris is, except for its extreme helium deficiency, similar to the He weak sn star HD 21699. A unique period for the magnetic and C IV…
The Temperature Scale of Hot DA White Dwarfs: Temperatures from Far-Ultraviolet Continuum Fluxes
Basri, Gibor; Bowyer, Stuart; Finley, David S.
Observed far-UV to visible flux ratios of all DA white dwarfs hotter than about 25,000 K are compared with ratios predicted by models in order to derive effective temperatures for the stars. All suitable IUE spectra of seven hot DA white dwarfs for which accurate temperatures based on hydrogen line profiles were available are used to derive a flux…
Correlation of X-Ray Burst Properties with Source State in the ``Atoll'' Source 4U/MXB 1636-53
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +3 more
A series of Exosat observations of the 'atoll' source 4U/MXB 1636 - 53 shows that duration and temperature of the X-ray bursts strongly correlate with the X-ray spectral and fast variability characteristics of the persistent emission of the source. This implies that spectral shape, fast variability, and burst duration and temperature all correlate…
Evidence for a Supermassive Black Hole in the Nucleus of the Seyfert Galaxy NGC 5548
Crenshaw, D. Michael; Blackwell, James H., Jr.
The international campaign to monitor the variable Seyfert 1 galaxy NGC 5548 with the International Ultraviolet Explorer (IUE) has provided an extensive and well-sampled set of spectroscopic observations. These observations are used to study the response of the C IV λ1550 emission-line profile to changes in the photoionizing continuum. Near the en…
The Strength of Optical Fe II Emission in Quasi-stellar Objects
Zheng, Wei; O'Brien, Paul T.
Based on optical data for a sample of 33 QSOs taken from Wilkes and Elvis, we study the relation between the strength of optical Fe II emission, the line widths, and the soft X-ray spectrum. The previously claimed relation that objects with flat soft X-ray spectra have weak optical Fe II emission is not present for this sample. A strong relation e…
Chromospheres of Metal-deficient Field Giants
Smith, Graeme H.; Dupree, A. K.; Hartmann, L.
Observations of the 2800-A Mg II line have been obtained with IUE for a sample of 10 metal-deficient field giant stars to search for chromospheric emission and signatures of mass loss, as well as to establish the level of chromospheric radiative energy losses from these stars. Mg II emission is probably present in all stars. High-resolution spectr…
Spectral Synthesis in the Ultraviolet. III. The Spectral Morphology of Normal Stars in the Mid-Ultraviolet
O'Connell, Robert W.; Burstein, David; Wu, Chi-Chao +1 more
The morphology of 218 mid-UV spectra of stars ranging from O through K in spectral type is examined. Several new line and continuum indices are defined and their usefulness as temperature, luminosity, and metallicity discriminants is discussed. Mid-UV stellar continua are found to be markedly affected by abundance. A UV excess, delta(2600-V), is c…
MG II Observed in the Local Interstellar Medium: The Local Cloud
Molaro, P.; Beckman, J. E.; Vladilo, G. +1 more
Observations of interstellar absorptions superposed on the chromospheric Mg II emissions of nearby cool stars have been used to explore the structure of the local interstellar medium along many lines of sight. The interstellar cloud in which the sun is immersed (the 'local cloud', hereafter LC) has not previously been detected using this technique…
Ultraviolet Interstellar Absorption toward HD 163522, a Halo Star at 9 Kiloparsecs in the Direction L = 350 and B = -9
Savage, Blair D.; Sembach, Kenneth; Massa, Derck
UV interstellar absorption line measurements obtained by the IUE satellite toward HD 163522 in the direction l = 349.6 deg and b = -9 deg are analyzed. The UV stellar spectrum of HD 163522 places the star beyond the Galactic center at a distance away from the Galactic plane of z = -1.5 kpc. An absorption-line spectrum with S/N approximately equal …