Search Publications
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…
Dust density and mass distribution near comet Halley from Giotto observations
Grün, E.; Zarnecki, J. C.; Wallis, M. K. +25 more
The dust impact detection system (DIDSY) carried by the Giotto spacecraft has measured the density and mass spectrum (in the range 10-20-10-8 kg) of the dust near comet Halley. Profiles of the dust spectrum obtained at a distance of 291,000 km from the Halley nucleus show a complex mass spectrum, depleted in intermediate and …
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…
Distances to planetary nebulae. I. The reddening-distance method.
Pottasch, S. R.; Pel, J. W.; Gathier, R.
Distances to 12 planetary nebulae are derived from the increase of interstellar reddening with distance along the lines of sight of the nebulae. The reddening-distance relations are determined using Walraven VBLUW photometry of stars in small fields around the planetary nebulae. With a theoretical calibration of the VBLUW colors the effective temp…
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, …
Ion flow at comet Halley
Cerulli-Irelli, R.; Thomsen, M.; Johnstone, A. +25 more
The three-dimensional positive ion analyser aboard the Giotto spacecraft has been used to study the interaction between protons and α-particles in the solar wind and positive ions from comet Halley. Although the first impression of the overall structure is that the plasma flow evolves smoothly as the nucleus is approached, three sharp transitions …
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<…
Observations of type I X-ray bursts from CIR X-1.
Fabian, A. C.; Tennant, A. F.; Shafer, R. A.
EXOSAT has recently observed three X-ray bursts from the direction of Circinus X-1 which have all the properties of type I bursts. These bursts most likely originate from Cir X-1 and the authors therefore identify Cir X-1 as a neutron star and not a black hole. The properties of the new bursts, such as the ratio of the energy released between burs…
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 …
Doppler-shifted X-ray line emission from SS 433.
King, A. R.; Watson, M. G.; Brinkmann, W. +1 more
The authors present the results from a series of X-ray observations of SS433 made with the EXOSAT Observatory in 1983 - 1985 which show that strong iron line emission is present in its X-ray spectrum and displays large energy shifts which vary as a function of the 164-day precession phase. These energy shifts are entirely consistent with the Doppl…