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The Hipparcos space mission - A revolution in astronomy
Schuyer, Maurice
The Hipparcos mission to establish an accurate catalog of stellar atmospheric parameters for about 120,000 selected stars is presented. The selected stars cover a range that extends from magnitude -1.5 (for the brightest) to magnitude +12 (for the faintest). The scientific payload and the mission profile of the satellite, and the recent status of …
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 …