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EXOSAT Observations of the Rapidly Rotating Flare Star Gliese 890
Singh, K. P.; Rao, A. R.
This paper presents the first X-ray observations of the late-type dwarf flare star Gliese 890 using the low-energy (LE) and the medium energy (ME) detectors of the Exosat Observatory. A steady X-ray emission, most probably of coronal origin, is detected. No flaring activity is observed in X-ray observations. A combined spectral fit to the LE and M…
On the Interpretation of the EXOSAT Photometry of Two Hot DA White Dwarfs
Petre, Robert; Vennes, Stephane; Shipman, Harry L.
Exosat photometric observations of the hot DA white dwarfs GD 2 and EG 70 are presented and analyzed using model atmosphere and synthetic spectrum calculations. The numerical accuracy of the calculations and their impact on the reliability of the results are addressed. The optimum atmospheric parameters that explain the complete spectral coverage …
Chromospheric Variability of M Giant Semiregular Variables
Johnson, Hollis R.; Eaton, Joel A.; Cadmus, Robert R., Jr.
The results of monitoring the chromospheric emission from three M giant semiregular variables, W Cyg, NU Pav, and Theta Aps at low dispersion with the IUE satellite are reported along with high-dispersion IUE spectra for R Lyr and Delta(2) Lyr. The chromospheric emission is variable in all of the first three stars, and the Mg II strength generally…
Model Atmosphere Analysis of the DZ White Dwarf K789-37
Koester, D.; Kilkenny, D.; Wegner, G.
This paper presents new observations and an analysis using model atmosphere techniques of the recently discovered DZA white dwarf K789 - 37. The effective temperature derived is 9500 + or - 500 K. Abundances are determined for the elements hydrogen, magnesium, calcium, and iron, as well as upper limits for carbon and silicon. The abundances are ve…
Terminal Velocities of the Winds from Rapidly Rotating OB Stars
Friend, David B.
This paper presents measurements of terminal velocities of OB stars which are rapid rotators, based on archival high-dispersion IUE spectra of the C IV resonance doublet. The terminal velocities of the most rapidly rotating stars appear to be systematically lower than those of the less rapidly rotating stars (at least for the cooler stars), althou…
Ultraviolet Gas Absorption and Dust Extinction toward M8
Bohm-Vitense, Erika; Boggs, Don
Interstellar absorption lines are analyzed using high-resolution IUE spectra of 11 stars in the young cluster NGC 6530 located in the M8 region. High-velocity clouds at -35 km/s and -60 km/s are seen toward all cluster stars. The components arise in gases that are part of large interstellar bubbles centered on the cluster and driven by stellar win…
HD 51956: A Supergiant in an Interacting Binary
Parsons, Sidney B.; Ake, Thomas B.
IUE ultraviolet spectral observations reveal that the F supergiant HD 51956 contains a hot companion star partially obscured by warm plasma. Variable absorption features are analogous to those in the strongly interacting system HD 207739. The F type component is apparently transferring matter to a subluminous B type star which originally was the p…
EXOSAT Observations of the Suspected Flare Star BD +48 degrees 1958A
Singh, K. P.; Rao, A. R.; Vahia, M. N.
X-ray observations are reported for the BY Dra variable BD + 48 deg 1958A using the low-energy (LE) and the medium-energy (ME) detectors of Exosat. The star is detected in both the LE and the ME detectors, with some evidence for a long-duration (over 2-hr) X-ray flare. A combined spectral fit to the LE and ME data leads to an X-ray plasma temperat…
Fitting Improved Accretion Disk Models to the Multiwavelength Continua of Quasars and Active Galactic Nuclei
Malkan, Matthew A.; Sun, Wei-Hsin
We present fits to the ultraviolet-optical-infrared spectra of 60 quasars and active galactic nuclei (AGNs) using improved black hole accretion disk models. The disk is assumed geometrically thin and optically thick. We included the relativistic effects of disk inclination, including Doppler boosting, gravitational focusing, and gravitational reds…
Kinematic Evidence for a Relativistic Keplerian Disk: ARP 102B
Filippenko, Alexei V.; Halpern, Jules P.; Chen, Kaiyou
The broad emission lines of the elliptical galaxy Arp 102B have peaks which are significantly displaced in velocity with respect to the host galaxy of the active galactic nucleus (AGN). We calculated line profiles for a Keplerian disk, including relativistic effects which were not treated rigorously in previous papers. We found an excellent fit of…