Search Publications
The Discovery of a 685 second Orbital Period from the X-Ray Source 4U 1820-30 in the Globular Cluster NGC 6624
Stella, L.; Priedhorsky, W.; White, N. E.
The discovery of a coherent 685 s periodicity in the X-ray source 4U 1820 -30, which is located in the globular cluster NGC 6624, is reported. The modulation has a peak-to-peak amplitude of up to 3 percent and was independently detected in three observations by the EXOSAT Observatory. This period is unlikely to represent the rotation of a neutron …
Chromospheric-Coronal Activity at Saturated Levels
Walter, Frederick M.; Vilhu, Osmi
High-resolution IUE observations of Mg II emission lines in W Ursae Majoris were obtained. In addition, estimates of the Mg II emission for other F-type contact binaries were obtained using archival high-resolution k line spectra and some nonstandard methods; the available data were compiled for Mg II, C IV, and X-ray emission in main-sequence F, …
Highly Ionized Interstellar Gas Located in the Galactic Disk and Halo
Savage, Blair D.; Massa, Derck
High-resolution IUE absorption line spectra have been obtained for 40 distant stars in order to study the distribution of interstellar H I, Si IV, C IV, and N V in the Galactic disk and lower halo. Respective midplane densities of 2 x 10 to the -9th, 7 x 10 to the -9th, and 3 x 10 to the -9th are found for Si IV, C IV, and Ni V. Both column densit…
The Planetary Nebula NGC 3918
Harrington, J. P.; Walsh, J. R.; Barlow, M. J. +1 more
A detailed study of the planetary nebula NGC 3918, based on UV, optical, and radio observations, is presented. The central star has a predicted V magnitude of 14.6 and a luminosity of 6000 solar luminosities for a distance of 1.5 kpc. A contour map of the nebula in H-beta light is given. Velocity profiles of forbidden O II optical lines show that …
X-Ray Spectra of PG Quasars. II. The X-Ray--Ultraviolet Excess of PG 1211+143
Elvis, Martin; Green, Richard F.; Bechtold, Jill +2 more
Observations of the quasar PG 1211 + 143 are presented and its continuum is modelled in terms of an accretion disk and an underlying power law. The X-ray spectrum in the Einstein imaging proportional counter band is well described by a power law with the very steep spectral index 2.2 + or - 0.4. The overall continuum spectral energy distribution c…
On the Evolution and Activity of Cometary Nuclei
Bar-Nun, A.; Prialnik, D.
The thermal evolution of a spherical cometary nucleus (initial radius of 2.5 km), composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. This transition does not …
A Detailed Study of the C IV lambda 1550 Line Profile and Adjacent Spectral Features in NGC 4151 from 1978 to 1983
Perola, G. C.; Altamore, A.; Boksenberg, A. +7 more
The 1450 - 1720 Å spectral region of NGC 4151 is analyzed by means of Gaussian decomposition for 69 different epochs, from early 1978 to the end of 1983. The C IV λ1550 emission profile is well represented by a core, whose full width at half-maximum varies between 2600 and 5500 km s-1, and an ultrabroad component (14,600 km s-1
On the Theory of Type I X-Ray Bursts. The Energetics of Bursts and the Nuclear Fuel Reservoir in the Envelope
Lewin, Walter H. G.; Fujimoto, Masayuki Y.; Sztajno, Mirek +1 more
A comparison is made between the observed properties of type I X-ray bursts from 4U/MXB 1636-53 and those of models of thermonuclear flashes on accreting neutron stars. Possible explanations of variations in the burst recurrence properties without an apparent correlation with accretion rate are discussed. The strongest bursts with photospheric exp…
IUE Observations of the Dwarf Nova HL Canis Majoris and the Winds of Cataclysmic Variables
Raymond, John C.; Mauche, Christopher W.
In order to investigate the nature of the winds of cataclysmic variables the authors present an observational and theoretical study of the P Cygni profiles of these systems, giving particular attention to the profiles of the dwarf nova HL CMa. After presenting the IUE observations of HL CMa, the authors give the results of a synthetic spectral cod…
Intensity and Source State Dependence of the Quasi-periodic Oscillations in Scorpius X-1
Stella, L.; Parmar, A. N.; van der Klis, M. +2 more
Quasi-periodic oscillations (QPO) at 6 Hz were discovered from EXOSAT observations of Sco X-1 in its quiescent state by Middleditch and Priedhorsky. The authors report here on the properties of the QPO seen in earlier EXOSAT observations of Sco X-1. During these observations QPO were also detected when Sco X-1 was in an active state, in ≡20 minute…