Search Publications
Phase-resolved IUE Observations of AM Herculis System E1405-451
Nousek, J. A.; Takalo, L. O.
The authors report the first phase-resolved IUE observations of the AM Herculis system E1405-451. The spectra show bright emission lines from N V, C IV, and He II, whose centroids vary drastically during the 101.5 minute period. The radial velocities measured from the line centroids show a sinusoidal variation with a semi-amplitude of 300 km s
IUE--IRAS Studies of the Infrared Cirrus
Shull, J. Michael; van Steenberg, Michael E.
The authors have studied correlations of IRAS infrared cirrus fluxes with interstellar parameters toward 256 OB stars observed with IUE. The 60 and 100 µm fluxes correlate with N(H I), n, E(B - V), spectral type, vertical distance from the Galactic plane, and general UV illumination. No correlation was found with abundances of Si, Mn, Fe, S,…
EXOSAT Observations of the Hot Gas in the A1060 Cluster of Galaxies
Singh, K. P.; Westergaard, N. J.; Schnopper, H. W.
We have used the EXOSAT Observatory to map and to obtain the X-ray spectrum of the hot gas in the A1060 cluster of galaxies. The density and temperature profiles of the intracluster gas have been determined by spherical deprojection of the X-ray surface brightness distribution obtained. We assume hydrostatic equilibrium and a cluster gravitational…
The Extended Atmosphere of lambda Pavonis at the Time of the Emergence of H-Emissions from Minimum Intensity
Cidale, Lydia; Sahade, Jorge; Kondo, Yoji +2 more
A study of the Be star λ Pavonis, particularly of the changes in the Balmer discontinuity in the interval 1949 - 1982, is presented. Nearly simultaneous observations carried out with the ESO 1.5 m reflector at La Silla and with the IUE satellite correspond to an epoch when the H emission is starting to increase in intensity immediately after havin…
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 …