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Iron Abundance in the Hot DA White Dwarfs Feige 24 and G191 B2B
Thorstensen, John R.; Bowyer, Stuart; Vennes, Stephane +2 more
Attention is given to model calculations of the far- and extreme-UV line spectra of highly ionized Fe species (Fe IV, Fe V, and Fe VI) for hot high-gravity H-rich stars. A spectral analysis of 31 hr of exposure of the DA white dwarf Feige 24 with IUE in the echelle mode reveals the presence of Fe with an abundance relative to H by number of (5-10)…
The Interstellar Deuterium-to-Hydrogen Ratio: A Reevaluation of Lyman Absorption-Line Measurements
McCullough, Peter R.
The D/H ratio in the local interstellar medium is evaluated based upon previously published measurements of Lyman absorption lines together with the hypothesis that the D/H ratio is constant. A unique value for the D/H ratio of 1.5 (+/- 0.2) x 10 exp -5 by number is shown to be consistent with all published determinations made with the Copernicus …
Tomographic Separation of Composite Spectra. I. The Components of Plaskett's Star
Wiggs, Michael S.; Gies, Douglas R.; Bagnuolo, William G., Jr.
The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correlation analysis, which showed that the secondary produces significant lines in the UV, indicate…
Preliminary Analysis of an Ultraviolet Hubble Space Telescope Faint Object Camera Image of the Center of M31
Boksenberg, A.; Barbieri, C.; Weigelt, G. +17 more
A 5161 s exposure was taken with the FOC on the central 44" of M31, through a filter centered at 1750 A. Much of the light is redleak from visible wavelengths, but nearly half of it is genuine UV. The image shows the same central peak found earlier by Stratoscope, with a somewhat steeper dropoff outside that peak. More than 100 individual objects …
The Ultraviolet Absorption Spectrum of the Quasar H1821+643 (z = 0.297)
Schneider, Donald P.; Green, Richard F.; Jannuzi, Buell T. +2 more
We report measurements of the absorption lines in the ultraviolet spectrum of the nearby luminous quasar H1821+643 (z = 0.297). The results were obtained using high-resolution observations with the faint object spectrograph of the Hubble Space Telescope. A total of 51 absorption lines and a number of emission features were detected between 1190 an…
The Constitution of the Atmospheric Layers and the Extreme Ultraviolet Spectrum of Hot Hydrogen-rich White Dwarfs
Vennes, Stephane
An analysis is presented of the atmospheric properties of hot, H-rich, DA white dwarfs that is based on optical, UV, and X-ray observations aimed at predicting detailed spectral properties of these stars in the range 80-800 A. The divergences between observations from a sample of 15 hot DA white dwarfs emitting in the EUV/soft X-ray range and pure…
The Hubble Space Telescope Observations of X-Ray Nova MUSCAE 1991 and Its Spectral Evolution
Panagia, N.; Horne, Keith; Shrader, C. R. +4 more
Hubble Space Telescope Faint Object Spectrograph (FOS) Faint Object Camera (FOC) and observations of Nova Muscae 1991 obtained on May 14-15, 1991 are presented and discussed. A nearly featureless continuum with broad 2200 A absorption feature and no Balmer jump is found. The FOS spectrum is modeled, including previous multiepoch IUE, optical, and …
Time Series Observations of O Stars. I. IUE Observations of Variability in the Stellar Wind of zeta Puppis
Howarth, I. D.; Bolton, C. T.; Prinja, R. K. +7 more
Stellar wind variability in Zeta Pup (O4 I(n)f) is described based on 31 high-resolution IUE observations secured over 5 1/2 days in 1989 April. Extensive changes are evident in the absorption regions of Si IV 1393.76, 1402.77A and N IV 1718.55A P Cygni profiles. Both lines exhibit similar patterns of variability, which are characterized by the de…
A Survey of Ultraviolet Variability in Blazars
Edelson, Rick
This is the first comprehensive consistent survey of the ultraviolet variability properties of a large sample of blazars. All of the 14 blazars with five or more observations in a single IUE, camera showed significant variability. The strength of the ultraviolet variability is positively correlated with both the apparent ultraviolet luminosity and…
An Interpretation of the Spectral Properties of Hot Hydrogen-rich White Dwarfs with Stratified H/He Model Atmospheres
Vennes, Stephane; Fontaine, Gilles
A grid of stratified H/He model atmospheres applicable to the interpretation of the spectral properties of hot H-rich white dwarfs (WDs) is computed. Samples of hot DA WDs observed with Exosat and Einstein are analyzed using the models. Six out of six objects with T(eff) = 35,000 K or less do not show a EUV/soft X-ray flux deficiency and therefore…