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Observation of the Onset of an Emission Episode in the Be Star MU Centauri
Peters, G. J.
A series of recent CCD observations which shows the rapid development of Hα emission in the pulsating, transient Be star µ Cen in only 2 days and thus establishes a time scale for the physical changes in the photosphere that lead to the outburst, are presented. On 1985 March 25, Hα was in pure absorption in µ Cen but by 1985 March 27 a…
A 6 Second Periodic X-Ray Source in Carina
Charles, P. A.; Smale, A. P.; Seward, F. D.
A serendipitous source, 1E 1048.1-5937, was discovered during Einstein imaging observations of the Carina nebula. On July 13, 1979, this source had an intensity of 0.14 IPC counts/s, and the signal was 65 percent pulsed with a period of 6.44 s. An earlier observation failed to detect any source with strength greater than 1/10 the above signal. The…
The Ultraviolet Excess of Quasars. III. The Highly Polarized Quasars PKS 0736+017 and PKS 1510-089
Malkan, M. A.; Moore, R. L.
Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736 + 047 and PKS 1510 089 is analyzed. A blazer continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510 - 089, and at least three-quarte…
The Statistical Equilibrium of Hydrogen and Helium in a Radiation Field, with an Application to Interpreting Wolf-Rayet Spectra
Bhatia, A. K.; Underhill, A. B.
A 70-level model helium atom which includes singly and doubly excited states of He I and a 17-level model hydrogen atom are used to solve the equations of statistical equilibrium for helium and hydrogen in a radiation field. The plasma has a velocity gradient, and densities and temperatures typical for the mantles of Wolf-Rayet stars. The emission…
Rapid X-ray variability of the Seyfert galaxy MCG -6-30-15.
Turner, T. J.; Warwick, R. S.; Pounds, K. A.
Strong and continuous variability was detected in the X-ray emission of the Seyfert I galaxy MCG-6-30-15 during a 9 hr EXOSAT observation in July 1984. Changes in the 2-6 keV flux appear quasi-sinusoidal with a modulation depth of 40-50 percent and peak-to-trough time-scales as short as 1500 s. Although less well determined, due to a lower countin…
GX 339-4 : EXOSAT observations in the off and soft states.
Chiappetti, L.; Motch, C.; Ilovaisky, S. A. +1 more
Exosat observations of the highly variable low-mass X-ray binary GX 339-4, obtained with the low-energy telescope and channel-multiplier array in the off state on Apr. 25, 1985, and with the medium-energy Ar proportional counters and collimator array in the off state in Apr. 29, 1985, and in the soft state on May 7, 1984, are reported. The data ar…
Detection of broad ultraviolet Fe II lines in the spectrum of NGC 1068.
Boksenberg, A.; Snijders, M. A. J.; Netzer, Hagai
Ultraviolet observations of the nucleus ofo NGC 1068, obtained by the IUE over a period of 5 yr, are combined to give a high signal-to-noise spectrum of this source. The ultraviolet stellar continuum, obtained by comparison with ground-based data, is subtracted to show the nuclear nonstellar component. The resulting spectrum shows clearly the pres…
Neutron star model atmospheres - a comparison with MXB 1728-34.
Fabian, A. C.; Ross, R. R.; Foster, A. J.
A detailed comparison between the X-ray spectra calculated for model atmospheres in neutron stars and the observed spectra of X-ray bursts is presented. Comptonization and free-free absorption and emission processes are taken into account, as are the effects of iron in its last three states of ionization. Two types of model are formulated, a const…
Identification of two southern X-ray emitting cataclysmic variables.
Buckley, D. A. H.; Schwartz, D. A.; Tuohy, I. R. +2 more
The optical identification of two faint HEAO 1 X-ray sources with previously uncataloged cataclysmic variables is reported. The two cataclysmic variables, 1H 0542 - 407 and H0534 - 581, have average V magnitudes of about 15.7 and about 14.9, and have similar high excitation spectra with moderate to strong He II 4686 A emission. X-ray measurements …
Optical probing of comet Halley from the Giotto spacecraft
Llebaria, A.; Lamy, P.; Bertaux, J. L. +7 more
The Halley optical probe experiment (HOPE) aboard the Giotto spacecraft has provided the first measurements of the optical properties of the dust and of some gaseous species (CN, C2, CO+ and OH) from inside the coma of comet Halley. The dust spatial distribution, inferred from sunlight scattering, obeys an r-2 law …