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Cometary Grain Scattering versus Wavelength, or, ``What Color Is Comet Dust?''
Jewitt, David; Meech, Karen J.
Optical and near-infrared observations of comets are combined in a systematic study of the wavelength dependence of the scattering from cometary grains. The normalized rate of change of the reflectivity of cometary grains with respect to the wavelength of observations decreases as the wavelength increases. The observed wavelength dependence of the…
New Results on the X-Ray Emission and Its Correlation with the Ultraviolet in NGC 4151
Piro, L.; Perola, G. C.; Altamore, A. +8 more
Results from observations of the Seyfert galaxy NGC 4151 obtained with Exosat (0.1-25 keV) and IUE (1200-3000 A) during November 1983, and between December 1984 and January 1985, are presented. The stability of the flux during large-scale variations in the UV and X-ray regions suggests that the soft X-ray excess noted by Holt et al. (1980) represe…
Spectroscopic Studies of Wolf-Rayet Stars. III. The WC Subclass
Conti, P. S.; Massey, P.; Torres, A. V.
Wolf-Rayet (W-R) stars, which are the descendants of massive O-type stars, can be subdivided into three groups depending on their spectral appearance. These groups include the nitrogen class (WN), the carbon class (WC), and the oxygen class (WO). The present paper is concerned with the WC stars. The assignment of WC subtypes has been based on visu…
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 …