Search Publications
The Analysis of Apparent Optical Depth Profiles for Interstellar Absorption Lines
Sembach, Kenneth R.; Savage, Blair D.
Attention is given to the apparent optical depth method, a procedure for analyzing interstellar absorption lines. Observed absorption-line profiles are converted into profiles of apparent optical depth, and apparent column density per unit velocity. By comparing the latter for a given interstellar species having two or more absorption lines which …
Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. I. an 8 Month Campaign of Monitoring NGC 5548 with IUE
Mazeh, T.; Glass, I. S.; Malkan, M. A. +54 more
We present emission-line and ultraviolet continuum observations of a type I Seyfert galaxy in which the time resolution is adequate for describing the character of variability. Using the IUE satellite, the nucleus of NGC 5548 was observed every 4 days for a period of 8 months. Its mean properties-continuum shape, line ratios-are not unusual for ty…
Ultraviolet Variability of NGC 5548: Dynamics of the Continuum Production Region and Geometry of the Broad-Line Region
Malkan, M. A.; Kriss, G. A.; Horne, Keith +3 more
We used the data obtained in the 1989-1990 IUE monitoring of NGC 5548 to derive a mean shape for the ionizing spectrum; mean line profiles; the continuum fluctuation power spectrum in three UV bands; cross-correlation functions relating these bands; cross-correlation functions relating fluctuations in eight emission lines to fluctuations in the UV…
EXOSAT observations of clusters of galaxies - I. The X-ray data.
Edge, A. C.; Stewart, G. C.
X-ray observations of 45 clusters of galaxies made with the European X- ray Observatory Satellite, EXOSAT, are presented. The 0.1-20 keV spectra obtained constitute the largest homogeneous spectral sample presently available. Here the analysis of the spectral and imaging data is described. A significant scatter in the correlation between the X-ray…
Properties of the SN 1987A Circumstellar Ring and the Distance to the Large Magellanic Cloud
Panagia, N.; Kirshner, R. P.; Macchetto, F. +2 more
We have determined the distance to SN 1987A by comparing the angular size of its circumstellar ring, measured from an HST image obtained in a narrow [O III] 5007 A filter, with its absolute size derived from an analysis of the light curves of narrow UV lines (N V λ1240, N IV] λ1486, N III] λ1750, and C III] λ1909) measured with IUE. Our analysis c…
EXOSAT observations of clusters of galaxies - II. X-ray to optical correlations.
Edge, A. C.; Stewart, G. C.
The results obtained for clusters of galaxies using X-ray data from the European X-ray Observatory Satellite, EXOSAT, are compared with the optical, infrared and radio properties of the clusters taken from the literature. A number of strong correlations are found. The ratios of the intracluster medium (ICM) temperature and the cluster velocity dis…
The Chromospheric Emission--Age Relation for Stars of the Lower Main Sequence and Its Implications for the Star Formation Rate
Soderblom, David R.; Duncan, Douglas K.; Johnson, Dean R. H.
An attempt is made to formulate the relationship between age and chromospheric emission (CE) in late-type dwarf stars. Evidence is reviewed that a deterministic relationship of this type actually exists, and that for stars of known age, either a power-law relation or a curve corresponding to a constant star formation rate fits equally well. Furthe…
The Great Flare of 1985 April 12 on AD Leonis
Hawley, Suzanne L.; Pettersen, Bjorn R.
A giant flare on the M dwarf star AD Leo is examined on the basis of photometric and spectroscopic observations covering the wavelength range 1200-1800 A. A flare energy budget over the entire optical and ultraviolet wavelength region is constructed as a function of time during the flare. The continuum radiation is shown to be the dominant source …
Temperature and luminosity of hot components in symbiotic stars.
Vogel, M.; Nussbaumer, H.; Schmid, H. M. +1 more
Typical radiation temperatures and luminosities are derived for the hot component of a representative sample of symbiotic systems by adapting the Zanstra method to the special requirements of symbiotic stars. Temperatures are derived by comparing the He II 1640 nebular recombination line with the underlying continuum. Particle-bounded and radiatio…
On Winds and X-Rays of O-Type Stars
Chlebowski, Tomasz; Garmany, Catharine D.
The dependence between stellar wind parameters and their X-ray fluxes is studied. Bolometric corrections are examined as a function of temperature, and a bolometric luminosity scale is proposed for the O-type stars. New mass-loss rates and terminal velocities of 40 well-known, bright single stars or binaries are measured, and the Lyman-alpha profi…