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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…
An Analysis of the Shapes of Ultraviolet Extinction Curves. III. an Atlas of Ultraviolet Extinction Curves
Fitzpatrick, Edward L.; Massa, Derck
The basic data needed to produce UV extinction curves for a sample of 78 stars, including spectral types, visual photometry, parameters used to produce fits to the UV extinction curves, distances to the program stars, and line-of-sight H I column densities, are presented. The observational and numerical techniques used to obtain the results are di…
Multi-frequency variations of the Wolf-rayet system HD 193793 - I. Infrared, X-ray and radio observations.
van der Woerd, H.; van der Hucht, K. A.; Pollock, A. M. T. +3 more
Observations made of the Wolf-Rayet system HD 193793 over the 1979-1989 period in the radio, X-ray, and IR regions reveal great variations in all three regimes. The most complete coverage obtained was in the IR; attention is given to an IR outburst in 1985 during which the IR flux increased by as much as an order of magnitude over the course of se…
Observations of Cygnus X-2 with IUE : ultraviolet results from a multiwavelength campaign.
Raymond, J. C.; Hasinger, G.; Verbunt, F. +3 more
IUE observations of Cyg X-2 obtained during June and October 1988 are reported and analyzed, with reference to data from simultaneous X-ray and radio observations and the predictions of theoretical models. The results are presented in extensive tables and graphs and characterized in detail. The UV flux is shown to increase monotonically as the X-r…
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…
The ultra-compact broad emision line region in NGC 4151.
Perola, G. C.; Boksenberg, A.; Penston, M. V. +6 more
New observations of the UV continuum and emission lines of a Seyfert I galaxy are presented in which the time resolution is adequate to describe the character of variability. Using the IUE satellite, the nucleus of NGC 4151 was observed with a mean interval of 3.4 d during 2 months. The flux of the continuum and of most emission lines underwent la…
The Ultraviolet Calibration of the Hubble Space Telescope. IV. Absolute IUE Fluxes of Hubble Space Telescope Standard Stars
Bohlin, Ralph C.; Gry, Cecile; Holm, Albert V. +1 more
UV fluxes are presented for 37 stars selected as calibration standards for the Hubble Space Telescope (HST). In order to provide data of maximum precision, new absolute calibrations have been derived for the IUE SWP and LWR cameras for point sources in the large apertures, while the sensitivities of the trail and small aperture observing modes rel…
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…