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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…
He I absorption lines in high-redshift Lyman limit systems of the QSO HS 1700+6416.
Reimers, D.; Vogel, S.
We report the detection of He I resonance lines in four high- redshift Lyman limit systems of the QSO HS 1700+6416 (z = 2.72) observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We find neutral hydrogen to neutral helium column density ratios N_HI_/N_HeI_ ~ 30 (possible range 20 to 70). Ionization calculations using CL…
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…
The Abundance of Ammonia in Comet P/Halley Derived from Ultraviolet Spectrophotometry of NH by ASTRON and IUE
Feldman, P. D.; Grinin, V. P.; Fournier, K. B. +1 more
From an analysis of the spatial profiles of both the NH and OH UV emissions observed by the ASTRON satellite, the ratio of ammonia-to-water production rates in Comet Halley on April 9, 1986 is derived and found to lie in the range of 0.44-0.94 percent. In order to compare this result with those based on both ground-based and in situ observations m…
Simultaneous GINGA and IUE Observations of the Seyfert Galaxy NGC 3516
Koyama, Katsuji; Halpern, Jules P.; Awaki, Hisamitsu +2 more
Simultaneous X-ray and UV observations of the Seyfert 1 galaxy NGC 3516 were carried out to investigate the connection between the variable X-ray and ultraviolet absorption features. Over a 2 week period, X-ray spectra Were obtained with Ginga, simultaneously with UV spectra from IUE. The X-ray spectrum was complex and could be fitted satisfactori…
The evolution of the interplanetary sector structure in 1992
Balogh, A.; Forsyth, R. J.; Smith, E. J. +1 more
The unique vantage point of the Ulysses spacecraft throughout 1992 and the beginning of 1993, at a close to constant heliocentric distance of about 5 AU and a slowly varying heliographic latitude from 5° to 30° south is used to describe and discuss the evolution of the sector structure of the interplanetary magnetic field during the declining phas…
LSIV -12 degrees 111: A Candidate Halo Proto--Planetary Nebula
Dufton, P. L.; Keenan, F. P.; Conlon, E. S. +1 more
We report on multiwavelength observations of LSIV -12 deg 111, which may be an emerging halo planetary nebula. This object was previously classified as a young emission-line B-type star, but a model atmosphere abundance analysis of high-resolution optical spectra has revealed it to be an evolved object, probably in the postasymptotic giant branch …
IUE Temperatures for White Dwarf Stars in and Around the ZZ Ceti Instability Strip
Kepler, S. O.; Nelan, E. P.
We have analyzed all the archival IUE images of the DA4 and DA5 white dwarfs with model atmosphere fluxes incorporating the quasi-molecular opacities to obtain a consistent set of temperatures for both the variables and nonvariables in and around the ZZ Ceti instability strip. We have found four nonvariable stars inside the instability strip. Take…
A detailed X-ray and radio study of the supernova remnant W 44.
Angelini, Lorella; Jones, L. R.; Smith, A.
We analyze EXOSAT and Einstein Observatory X-ray spectra, an Einstein X-ray image, and a detailed VLA radio map of the SNR W44. The diffuse soft X-ray emission, which is only observed from the interior of the SNR, is shown to be largely of thermal origin. The absence of soft X-ray emission from the shell can be explained by the measured line-of-si…
Hubble Space Telescope Images of the Subarcsecond Jet in DG Tauri
Yang, C.; Hartigan, P.; Kepner, J. +1 more
We have applied a new restoration technique to archival [O~I], H$\alpha$, and continuum HST images of DG~Tau. The restored [O~I] and H$\alpha$ images show that DG~Tau has a jet with a projected length of 25~AU and width $\leq$10~AU, and is already collimated at a projected distance of $\sim$~40~AU (0\farcs25) from the star. Such a narrow width and…