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Dynamic Processes in Be Star Atmospheres. III. Rapid Multiwavelength Variability in gamma Cassiopeiae
Smith, Myron A.
A review of the characteristics of X-ray emission from gamma Cas suggests various weaknesses with conventional scenarios that invoke Be wind interactions with a putative binary companion. To explore whether this emission might arise instead from sporadic high-energy events on the Be star itself, we have examined the temporal behavior of Voyager 1 …
Late-Time Spectra and Type IA Supernova Models: New Clues from the Hubble Space Telescope
Schmidt, B. P.; Kirshner, R. P.; Wheeler, J. C. +4 more
Calculated late-time spectra of two classical hydrodynamical models for Type Ia supernovae (deflagration model WI of Nomoto, Thielemann, & Yokoi, and delayed detonation model DD4 of Woosley & Weaver) are compared with observations of SN 1992A and other spectroscopically normal SNe Ia, An important new piece of information is provided by ob…
Molecular H 2 Emission in HH 47A: Hubble Space Telescope GHRS and FOC Observations
Hartigan, Patrick; Raymond, John C.; Curiel, Salvador +4 more
We present Hubble Space Telescope ultraviolet observations of the bow shock at the end of the HH 47 stellar jet obtained with the Goddard High Resolution Spectrograph (GHRS) and the Faint Object Camera (FOC). The GHRS spectrum shows three prominent emission lines of H2 which are produced by Lyα fluorescence and one line that we cannot i…
Astro-1 and Ground-based Observations of Markarian 335: Evidence for an Accretion Disk
Malkan, M. A.; Zheng, W.; Kriss, G. A. +8 more
Simultaneous UV and optical observations of the Seyfert galaxy Markarian 335 (z = 0.026) during the Astro-1 mission yield a spectrum spanning the wavelength range of 912-8410 A. In the sub-Lyα region a prominent blended emission feature of O VI λλ1032, 1038, and Lyβ is nearly as strong as C IV λ1549. The continuum flux extends beyond the redshifte…
Fine-Scale Filamentary Structure in Coronal Streamers
Bird, Michael K.; Woo, Richard; Armstrong, John W. +1 more
Doppler scintillation measurements of a coronal streamer lasting several solar rotations have been conducted by Ulysses in 1991 over a heliocentric distance range of 14--77 R0. By showing that the solar corona is filamentary, and that Doppler frequency is the radio counterpart of white-light eclipse pictures processed to enhance spatial gradients,…
Emission Spectrum Integrated over an Accretion Disk: Comparison with Observations of Active Galactic Nuclei
Shimura, Toshiya; Takahara, Fumio
Emission spectrum from an accretion disk for active galactic nuclei is obtained by solving the vertical structure and radiative transfer self-consistently and by integrating the local spectrum over radii. We found that even for moderate accretion rates, disks emit a significant portion of the total luminosity in UV through soft X-ray range; for th…
Gas Phase Abundances and Conditions along the Sight Line to the Low-Halo, Inner Galaxy Star HD 167756
Sembach, Kenneth R.; Savage, Blair D.; Cardelli, Jason A.
We present high-resolution (3.5 km/s) Goddard High Resolution Spectrograph (GHRS) measurements of the Mg II, Si II, Cr II, Fe II, and Zn II lines toward HD 167756, a low-latitude halo star at a distance of 4 kpc in the direction l = 351.5 deg, b = -12.3 and at a Galactic altitude of z = -0.85 kpc. Supplemental Na I, Ca II, and H I data are also pr…
Cataclysmic and Close Binaries in Star Clusters. II. Probing the Core of NGC 6752 with Hubble Space Telescope
Drissen, Laurent; Paresce, F.; Shara, Michael M. +1 more
The cores of globular clusters have been predicted to be rich in close, interacting binaries. We have used the Hubble Space Telescope (HST) to test this prediction by monitoring 730 stars in the core of NGC 5752 for rapid variability. Thirty-one Faint Object Camera (FOC) images at 2200 A, with time resolution of 11 minutes, and spanning 7 hr have …
Ultraviolet Observations of the Eruption in the Small Magellanic Cloud Wolf-Rayet System HD 5980
Koenigsberger, Gloria; Georgiev, Leonid; Guinan, Ed +1 more
We present results of IUE observations ( lambda lambda 1200--3200) of the erupting system HD 5980 obtained in 1994 November and December. The 1994 spectrum presents emission lines from ions such as N III, Si II--III and Al III which were absent in 1991. There is a systematic tendency towards higher degrees of ionization over the 44 days covered by…
Ultraviolet Observations of SW Ursae Majoris, BC Ursae Majoris, and TV Corvi (1217--18): IUE Spectroscopy and Outburst Light Curves
Szkody, Paula; Howell, Steve B.; Sonneborn, George +5 more
We present lUE superoutburst observations of three tremendous outburst amplitude dwarf novae. Limited ground-based optical photometry was also obtained contemporaneously. This is the first such ultraviolet spectroscopy of these systems, and we compare our results with other well-studied dwarf novae of similar orbital periods. We find that the slop…