Search Publications
Terminal Velocities for a Large Sample of O Stars, B Supergiants, and Wolf-Rayet Stars
Barlow, M. J.; Howarth, Ian D.; Prinja, Raman K.
It is argued that easily measured, reliable estimates of terminal velocities for early-type stars are provided by the central velocity asymptotically approached by narrow absorption features and by the violet limit of zero residual intensity in saturated P Cygni profiles. These estimators are used to determine terminal velocities, v(infinity), for…
Magnetically Controlled Circumstellar Matter in the Helium-strong Stars
Shore, Steven N.; Brown, Douglas N.
This paper reports the observation and interpretation of the ultraviolet spectrum variations of nine helium-strong stars: HD 36485, 37017, 37479, 37776, 58260, 60344, 64740, 96446, and 133518. A unified model is developed to account for the observed correlation among three stellar properties: the line profile characteristics of the C IV and Si IV …
A Study of the Baldwin Effect in the IUE Data Set
Koratkar, A. P.; Kinney, A. L.; Rivolo, A. R.
We have investigated the controversial relation between the continuum luminosity and the C IV λ1550 emission-line strength in the spectra of quasars, commonly referred to as the Baldwin Effect, as a possible indicator of absolute luminosity, We have used all available quasar spectra in the IUE archives which have C IV and/or Lyα shifted into the I…
Broad-Band Properties of the CfA Seyfert Galaxies. III. Ultraviolet Variability
Krolik, J. H.; Edelson, R. A.; Pike, G. F.
Six hundred fifty-seven archived IUE spectra are used to study the ultraviolet variability properties of the six members of the CfA Seyfert 1 galaxy sample with many repeated observations. All Show strong evidence for continuum and line variations. There is a tendency for less luminous objects to be more strongly variable. Most objects show a clea…
Optically Thin Thermal Emission as the Origin of the Big Bump in the Spectra of Active Galactic Nuclei
Peterson, B. M.; Korista, K. T.; Ferland, G. J.
The nature of the "big bump," the excess of ultraviolet emission seen in many active nuclei, is a clue to the source of the energy generation in the central regions of quasars. We report observations of the Seyfert galaxy Mrk 590, which show dramatic changes in both the continuum and hydrogen lines, thus offering a clue to the origin of the "big b…
Ultraviolet and Optical Variations in Active Galactic Nuclei: The Seyfert 1 Galaxy NGC 5548
Talavera, A.; Netzer, H.; Wamsteker, W. +8 more
We describe the results of a project to study the combined ultraviolet- optical spectrum of the Seyfert I galaxy NGC 5548 over the period 1978- 1986. Of the many spectrophotometric observations made with a typical resolution of 5-8 A, 11 epochs were simultaneous and nine cover the range from 1150 to 7000 A. The combined IUE and ground-based observ…
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 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…
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…