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High-Energy Spectrum of Cygnus X-1 Revisited
Done, C.; Fabian, A. C.; Matt, G. +1 more
The X-ray spectrum of Cyg X-1 is probably produced by thermal Comptonization in an accretion disk corona. Photons reflected from the disk are also Comptonized, so the predicted reflection spectrum is dependent on the optical depth and temperature of the scattering medium. Thus, observations of reflection in the 2-20 keV energy range can constrain …
Interstellar MG II and C IV Absorption toward Markarian 205 by NGC 4319: an ``Optically Thick'' QSO Absorption System
Bowen, David V.; Blades, J. C.
We have used the Goddard High-Resolution Spectrograph aboard HST to detect interstellar Mg II and C IV absorption lines toward Mrk 205, a QSO whose sightline passes within 3 h^-1^ kpc of the foreground galaxy NGC 4319. Absorption is detected from both local Milky Way gas and from NGC 4319, making this the first observation of an isolated, low-reds…
Ultraviolet Line Diagnostics of Accretion Disk Winds in Cataclysmic Variables
Shlosman, Isaac; Vitello, Peter
The IUE data base is used to analyze the UV line shapes of the cataclysmic variables RW Sex, RW Tri, and V Sge. Observed lines are compared to synthetic line profiles computed using a model of rotating biconical winds from accretion disks. The wind model calculates the wind ionization structure self-consistently including photoionization from the …
A Cluster of Nascent Galaxies at Z = 2?
Dressler, Alan; Oemler, Augustus, Jr.; Gunn, James E. +1 more
On a 6 hr Wide Field Camera exposure with the Hubble Space Telescope of the rich cluster CL 0939+4713, we have identified an apparent cluster of ~30 faint, extended objects with magnitudes 22 < r < 25. The objects are typically 1" in size with bright central regions only a few tenths of an arcsecond in size, and are distributed over a region…
Scattered Light in the Echelle Modes of the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope. II. Analysis of In-Flight Spectroscopic Observations
Ebbets, Dennis C.; Savage, Blair D.; Cardelli, Jason A.
We report on an analysis of observations made with the GHRS aboard the HST for the purpose of calibrating the effects of scattered light. The data were obtained during the first 2 years of flight operations as part of the Science Verification, Science Assessment Observations, and Guaranteed Time Observations programs. Both the general level of bac…
The Population of Massive Stars in R136 from Faint Object Camera Ultraviolet Observations
Leitherer, Claus; Nota, Antonella; de Marchi, Guido +2 more
New ultraviolet (λ ≃ 1300 Å, λ ≃ 3400 Å), HST Faint Object Camera observations have been used to derive the UV color-magnitude diagram (CMD) of R136. The main scientific goal is the study of the upper end of the stellar mass function at ultraviolet wavelengths where the color degeneracy encountered in visual CMDs is less severe.
The CMD has b…Detection of an Ultraviolet and Visible Counterpart of the NGC 6624 X-Ray Burster
Boksenberg, A.; Barbieri, C.; Weigelt, G. +18 more
We have detected, in images taken with the HST FOC, the UV and optical counterpart of the X-ray source 4U 1820-30 in the globular cluster NGC 6624. Astrometric measurements place this object 2 sigma from the X-ray position of 4U 1820-30. The source dominates a far-UV FOC image and has the same flux at 1400 A as was seen through the large IUE apert…
Chemical Composition of M8 Based on IUE and Visual Observations
Dufour, R. J.; Torres-Peimbert, S.; Peimbert, M.
We present optical and IUE observations of the Hourglass Nebula which is embedded in the galactic H II region M8. By comparing the intensities of the [C III] lines λλ1907 + 1909 with that of C II λ4267, a value of t2 = 0.046±0.01 is obtained. The logarithmic abundances by number of the gaseous component for t2 = 0.046 are: H …
Ultraviolet Observations of Selective Wind Eclipses in gamma Velorum and Evidence for Colliding Winds
Willis, A. J.; Stevens, I. R.; St. -Louis, N.
The paper presents an analysis of all IUE high-resolution spectra available in the archives of the WC8 + O9I binary system Gamma Velorum. The IUE data are supplemented by a series of FUV spectra obtained with the Copernicus satellite covering the whole orbital period. The data reveal substantial UV spectral variations confined to resonance and low…
EGRET Limits on High-Energy Gamma-Ray Emission from X-Ray-- and Low-Energy Gamma-Ray--selected Seyfert Galaxies
Michelson, P. F.; Nolan, P. L.; Thompson, D. J. +13 more
A sample of 22 Seyfert galaxies, 11 type 1 and two type 2 galaxies selected according to their X-ray fluxes in the AGN survey catalogs of EXOSAT and Ginga, two additional type 1 galaxies for which detections in low-energy gamma rays have been reported in the past, plus six more type 1 galaxies and one unclassified Seyfert that have been studied by…