Search Publications
X-Ray Eclipse Mapping of AR Lacertae
Parmar, A. N.; White, N. E.; Culhane, J. L. +2 more
Exosat data of the binary cycle of the eclipsing RS CVn system AR Lac are studied. The data reveal that at energies of less than 1 ke V a factor of 2 intensity modulation is detected and at energies greater than 1 ke V no orbital modulation is observed. The chi-squared and maximum entropy methods are used to model low-energy modulation. The relati…
Non--LTE Model Calculations for SN 1987A and the Extragalactic Distance Scale
Schmutz, W.; Hamann, W. -R.; Abbott, D. C. +2 more
We present model atmospheres for the first week of SN 1987A, based on the luminosity and density/velocity structure from hydrodynamic models of Woosley. The models account for line blanketing, expansion, sphericity, and departures from LTE in hydrogen and helium and differ from previously published efforts because our models represent ab initio ca…
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…