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Combined approach to the Hubble Space Telescope wave-front distortion analysis.
Roddier, Claude; Roddier, Francois
Stellar images taken by the Hubble Space Telescope at various focus positions have been analyzed to estimate wave-front distortion. Rather than using a single algorithm, the authors found that better results were obtained by combining the advantages of various algorithms. For the planetary camera, the most accurate algorithms consistently gave a s…
The Violent Interstellar Environment Around the Wolf-Rayet Star HD 192163
Nichols-Bohlin, Joy; Fesen, Robert A.
IRAS Skyflux IR images, high-dispersion IUE UV spectra, optical spectra, and optical interference filter images are used to investigate the nature of the interstellar environment around the Wolf-Rayet star HD 192163. IRAS images show an apparent 1.5 x 1.8 deg IR emission shell very nearly centered on HD 192163, which is designated G75.5+2.4. It is…
Implications of the Soft X-Ray versus Hard X-Ray Temporal Relationship in Solar Flares
Mariska, John T.; Li, Peng; Emslie, A. Gordon
We have calculated the time profiles of spatially integrated hard X-ray (30-500 keV) and soft X-ray (1-8 Å) emission in both thick-target electron-heated models, and bulk heated thermal models, of the impulsive phase of solar flares. For the thermal model, we find a serious difficulty: the time profiles of the 30-500 keV hard X-ray emission do not…
Hydrogen and Metal Absorption Lines in PKS 0405-123 From the Halos of Low Redshift Galaxies
Filippenko, Alexei V.; Bechtold, Jill; Blades, J. C. +6 more
Hubble Space Telescope ultraviolet spectra and ground-based optical spectra of the bright quasar PKS 0405 - 123 are used to identify two absorption-line systems probably produced by the halos of foreground galaxies. The quasar lies in a rich galaxy field. Loose groups of galaxies are present in the field at <z_1_> = 0.1669 and <z_2_> =…
The Center of Gravity and Density Profile of 47 Tucanae
Calzetti, D.; Paresce, F.; de Marchi, G. +1 more
From the analysis of HST-FOC images of the globular cluster 47 Tuc, we have determined the position of the center of gravity to be about 6 arcsec away from the luminosity center. The luminosity center is mainly determined by an 'asymmetry' in the luminosity distribution of the stars brighter than m(342) about 16.5. The density profile from the dyn…
Spectral analysis of extremely helium rich subdwarfs O-stars.
Dreizler, S.
The NLTE analyses of four extremely helium rich sdO stars based on high resolution, high S/N CASPEC spectra are presented. Effective temperatures, gravities and the abundances of H, He, C, N, O, Ne, Mg, and Si have been deter- mined. It is found that LSIV+1O°9, LSS 1274, and UV 0832-01 have very similar parameters: Teff = 445…
An X-Ray Excited Wind in Centaurus X-3
Stevens, Ian R.; Day, C. S. R.
We propose a new interpretation of the behavior of the notable X-ray binary source Centaurus X-3. Based on both theoretical and observational arguments (using EXOSAT data), we suggest that an X-ray excited wind emanating from the O star is present in this system. Further, we suggest that this wind is responsible for the mass transfer in the system…
An Occultation by Saturn's Rings on 1991 October 2-3 Observed With The Hubble Space Telescope
Bosh, A. S.; Dolan, J. F.; Nelson, M. J. +7 more
An occultation of the star GSC 6323-01396 (V = 11.9) by Saturn's rings was observed with the High-Speed Photometer on the Hubble Space Telescope (HST) on 1991 October 2-3. This occultation occurred when Saturn was near a stationary point, so the apparent motion of Saturn relative to the star was dominated by the HST orbital motion (8 km/s). Data w…
Variable C IV Absorption in the Seyfert Galaxy NGC 5548: A Connection to Broad Absorption Line Quasi-stellar Objects?
Shull, J. Michael; Sachs, Elise R.
This is the second in a series of papers examining variable absorption components in the broad emission lines of Seyfert 1 galaxies. In an IUE survey of a complete sample of CfA Seyfert galaxies, we find that at least 12% and perhaps as many as 27% of the objects show evidence of intrinsic absorption in C IV 1549. In this paper, we use data from a…
The beta Pictoris circumstellar disk. XV. Highly ionized species near beta Pictoris.
Deleuil, M.; Feldman, P. D.; Moos, H. W. +7 more
Temporal variations of the Fe II, Mg II, and Al III circumstellar lines towards Beta Pictoris have been detected and monitored since 1985. However, the unusual presence of Al III ions is still puzzling, since the UV stellar flux from an A5V star such as Beta Pic is insufficient to produce such an ion. In order to better define the origin of such a…