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Spectral Properties of Blazars. I. Objects Observed in the Far-Ultraviolet
Maraschi, L.; Tanzi, E. G.; Ghisellini, G. +1 more
All blazars observed with the IUE are studied and shown to form a well-defined subgroup according to their spectral properties. These properties are discussed with respect to theoretical models and are compared with those of quasars. Radio, ultraviolet, and X-ray fluxes are used to construct composite spectral indices, and systematic differences b…
Short-Term Spectral Variability in AB Aurigae: Clues for Activity in Herbig AE Stars. I. The Ultraviolet Lines of MG II and Fe II
Simon, Theodore; Boesgaard, Ann Merchant; Catala, Claude +1 more
IUE satellite monitoring of the Herbig Ae star AB Aur in 1982 and 1984, with attention to the variability of both the Mg II 2795 A wind profile and a number of Fe II UV lines, has indicated temporal variations in the Mg II blue wing velocity by 30-50 percent at both epochs. By contrast, the Fe II spectrum was constant in 1982, but variable in 1984…
The Bursting Behavior of the Transient X-Ray Burst Source EXO 0748-676: A Dependence between the X-Ray Burst Properties and the Strength of the Persistent Emission
Haberl, F.; Parmar, A. N.; White, N. E. +1 more
Between 1985 February 15 and July 19 EXOSAT made eight observations of the transient X-ray source EXO 0748-676. Within this time interval the persistent flux varied by a factor of 5 from a high to a low state and back to a high state. We observed 26 type I bursts, of which 22 were analyzed in detail. As the persistent flux decreased, the burst fre…
Multifrequency Observations of the Superluminal Quasar 3C 345
Bregman, Joel N.; Rieke, G. H.; Matthews, K. +27 more
The authors have investigated the continuum properties of the superluminal quasar 3C 345 with monitoring studies at radio, optical, infrared, and X-ray frequencies. The data presented here include optical, infrared, and radio measurements for a period of 20 yr, far-infrared fluxes obtained with IRAS, and X-ray fluxes taken with the Einstein Observ…
Temperatures for Hot and Pulsating DB White Dwarfs Obtained with the IUE Observatory
Hansen, C. J.; Winget, D. E.; Green, Richard F. +5 more
Ultraviolet energy distributions are presented for 12 hot, helium-atmosphere DB white dwarfs, including the four known pulsating stars which define an empirical DB instability strip. Temperatures are derived exclusively from fits to the ultraviolet energy distributions, especially in the λλ1200 - 2000 region which is most sensitive to temperature.…
On the Nature of the Dwarf Carbon Star G77-61
Liebert, James; Dahn, Conard C.; Mould, Jeremy +4 more
A variety of new astrometric, photometric, and spectrophotometric data are presented for the low-luminosity carbon star G77-61. The improved parallax yields Mv = +10.08±0.43, while the revised temperature estimate from infrared, optical, and ultraviolet fluxes in 4100 (+200, -300)K, yielding logL/L_sun; = -1.75±0.16. Most importantly, r…
Discovery of Rapid Quasi-periodic Oscillations in Scorpius X-1
Priedhorsky, W. C.; Middleditch, J.
The X-ray flux from Sco X-1 can vary quasi-periodically. Fourier analysis of 5-20 keV X-ray data taken while the source was quiescent shows a power density peak at 6 Hz, with a 2 Hz FWHM, and which corresponds to 5 percent of the flux (rms amplitude). No 6 Hz peak was observed when the source was more active, but rather a broad distribution of exc…
DA White Dwarf Effective Temperatures Determined from IUE Lyman-Alpha Profiles
Wesemael, F.; Holberg, J. B.; Basile, J.
The Lyman-alpha profiles of 12 DA white dwarfs have been obtained with the International Ultraviolet Explorer Satellite. Analysis of these profiles provides an improved, uniform, and relatively bias-free measure of effective temperature for these stars over the range 20,000-60,000 K. Simultaneous estimates of surface gravity yield a mean gravity o…
Interstellar Abundances in Dense, Moderately Reddened Lines of Sight. I. Observational Evidence for Density-dependent Depletion
Joseph, Charles L.; Crutcher, Richard M.; Snow, Theodore P., Jr. +1 more
The nature of dust-gas interactions, which are capable of modifying the size distribution of interstellar grains and thus causing changes in the selective extinction curve, are investigated through depletion studies. The gaseous abundances of 15 elements have been determined for several lines of sight toward moderately reddened stars, each having …
EXOSAT Observations of V471 Tauri: A 9.25 Minute White Dwarf Pulsation and Orbital Phase Dependent X-Ray Dips
Sion, E. M.; Guinan, E. F.; Swank, J. H. +3 more
New results obtained from a 28 hr continuous observation of V471 Tauri with the EXOSAT satellite are reported. The detection of soft X-ray fluxes from both the white dwarf and the K dwarf, the discovery of a 9.25 minute pulsation from the white dwarf, and the discovery of orbital phase-related soft X-ray dips are discussed. The dips may be correla…