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The Evolution of Radiation-dominated Stars. I. Nonrotating Supermassive Stars
Woosley, S. E.; Fuller, G. M.; Weaver, T. A.
The evolution of nonrotating supermassive stars (M approximately equal to or greater than 5 x 10 to the 4th solar masses) is examined in detail using the results of hydrodynamic calculations which include post-Newtonian approximations to general relativistic gravity, an equation of state which includes electron-positron pairs, and all relevant nuc…
EXOSAT Observations of the 35 Day Cycle of Hercules X-1: Evidence for Neutron Star Precession
Pietsch, W.; Kahabka, P.; Truemper, J. +2 more
Her X-1 was observed with Exosat throughout a 35 day cycle at about 4 day sampling intervals. These measurements include, for the first time, an accurate determination of the 1.24 s pulse profiles during the short-on state at the middle of the 35 day cycle. The data show a large change in the pulse profiles between the main and short-on states, su…
X-Ray Spectra of PG Quasars. I. The Continuum from X-Rays to the Infrared
Elvis, Martin; Green, Richard F.; Bechtold, Jill +5 more
Einstein IPC X-ray spectra for a sample of eight optically selected quasars from the Palomar Bright Quasar survey are presented. The quasars have a mean power law energy slope which in five individual cases is inconsistent with the value found in hard X-ray selection criterion rather than luminosity, redshift, or U-B color. New IUE and optical con…
Variability of Markarian 1018: Seyfert 1.9 to Seyfert 1
Cohen, Ross D.; Ake, T. B.; Foltz, Craig B. +2 more
Simultaneous IUE and optical spectrophotometry of the Seyfert 1.9 galaxy Markarian 1018 is presented. The strength of H-beta(broad) has increased by a factor of 6.6 in 4 yr, and the galaxy now shows strong broad UV and optical line emission similar to that seen in normal Seyfert 1 galaxies, but with markedly asymmetric line profiles. As in other v…
Bimodal Quasi-oscillatory and Spectral Behavior in Scorpius X-1
Stella, L.; Priedhorsky, W.; Lewin, W. H. G. +4 more
Exosat observations of Sco X-1 obtained using the Xe and/or Ar detectors for a total of about 80,000 s during four runs on August 24-27, 1985 are reported and analyzed. Two modes of quasi-periodic oscillations (QPOs) corresponding to the quiescent and active states of Sco X-1 and to two modes of spectral behavior are identified and characterized, …
An EXOSAT Observation of Quiescent and Flare Coronal X-Ray Emission from Algol
Parmar, A. N.; White, N. E.; Culhane, J. L. +4 more
X-ray emission from the Algol system is believed to originate in a corona associated with the K star. The authors have used the EXOSAT Observatory to make a 35 hr continuous observation centered on the occultation of the K star by the B star primary. The spectrum of the quiescent emission in the 1 - 10 keV band gives a temperature of 2.5×107<…
The New Magnetic White Dwarf PG 1031+234: Polarization and Field Structure at More than 500 Million Gauss
Green, Richard F.; Liebert, James; Schmidt, Gary D. +2 more
PG 1031+234 is a newly discovered rotating, magnetic white dwarf. Its optical light is highly polarized, Pmax ≈ 6%, Vmax ≈ -12%, and strongly modulated on the 3 hr 24 minute rotation period. Optical and UV spectrophotometry reveal a spectrum of diffuse absorption features which match Zeeman calculations of hydrogen in fields …
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…