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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…
The Comet Halley Dust and Gas Environment
Keller, H. U.; Gombosi, T. I.; Sekanina, Z. +8 more
Quantitative descriptions of environments near the nucleus of comet P/Halley have been developed to support spacecraft and mission design for the flyby encounters in March, 1986. To summarize these models as they exist just before the encounters, we review the relevant data from prior Halley apparitions and from recent cometary research. Orbital e…
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.…
IRAS spectra of planetary nebulae. III.
Pottasch, S. R.; Mo, J. E.; Preite-Martinez, A. +2 more
Measurements of the IRAS spectra of planetary nebulae are presented. The spectra cover the wavelength 7.5 to 23 microns. The lines observed are mainly from ions of neon and sulfur. The abundance of these two elements is determined and compared to results found in other astronomical objects. It is also found that the Ne(4+) ion, when present, is fo…
The acceleration of particles in the vicinity of comets
Ip, W. -H.; Axford, W. I.
The various processes capable of accelerating ions in the vicinity of comets as part of the comet/ solar wind interaction are considered. It is concluded that the most important are ion pick-up, adiabatic compression and second order Fermi acceleration in the turbulence associated with the interaction. Model particle spectra are calculated on the …
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…