Search Publications
Ultraviolet Polarimetry and Spectroscopy of the BL Lacertae Object PKS 2155-304
Anderson, Scott F.; Miller, Bryan W.; Smith, Paul S. +3 more
We present ultraviolet spectropolarimetry of the BL Lac object 2155 - 304. These observations were made using the Hubble Space Telescope and the Faint Object Spectrograph and, represent the first opportunity to study the wavelength dependence of the UV (1360-3300 A) linear polarization in a BL Lac object. Nearly simultaneous ground-based optical p…
Proof for a wind from the hot component in the symbiotic system EG Andromedae.
Vogel, M.
One of the most debated issue in symbiotic research concerns the nature of the hot component. In this Letter we give observational evidence that in the symbiotic binary EG And the hot compact star loses mass through a stellar wind. The wind velocity is ≈ 500 km s -1, and the mass loss rate is Mṡ ≈ 5 × 10-9 Msu…
Chromospherically active Stars. XI. Giants With Compact Hot Companions and the Barium Star Scenario
Henry, Gregory W.; Fekel, Francis C.; Busby, Michael R. +1 more
We have determined spectroscopic orbits for three chromsopherically active giants that have hot compact companions. They are HD 160538 (KO III + wd, P = 904 days), HD 165141 (G8 III + wd, P approximately 5200 days), and HD 185510 (KO III + sdB, P = 20.6619 days). By fitting an IUE spectrum with theoretical models, we find the white dwarf companion…
The Luminosity Dependence of the X-Ray Spectrum of the Transient 42 Second Pulsar EXO 2030+375
Parmar, A. N.; White, N. E.; Reynolds, A. P.
We report on the evolution in the X-ray spectrum of the transient X-ray pulsar EXO 2030 + 375 during part of an outburst in 1985 May-August. The overall continuum spectral shape is similar to that of other accreting pulsars and can be represented by a power-law spectrum modified at low energies by significant absorption and at high energies either…
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…