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Masses and Densities of Pluto and Charion
Null, G. W.; Owen, W. M.; Synnott, S. P.
We have analyzed HST Wide Field Camera CCD images of Pluto, Charon, and a background star to observe Pluto's barycentric motion and to determine the individual masses and bulk densities of Pluto and Charon. The most fundamental new result was an accurate solution for a previously undetermined parameter, the Charon/Pluto mass ratio q; the new solut…
Detection of an Ultraviolet and Visible Counterpart of the NGC 6624 X-Ray Burster
Boksenberg, A.; Barbieri, C.; Weigelt, G. +18 more
We have detected, in images taken with the HST FOC, the UV and optical counterpart of the X-ray source 4U 1820-30 in the globular cluster NGC 6624. Astrometric measurements place this object 2 sigma from the X-ray position of 4U 1820-30. The source dominates a far-UV FOC image and has the same flux at 1400 A as was seen through the large IUE apert…
Measurements of hot plasmas in the magnetosphere of Jupiter
Simnett, G. M.; Pick, M.; Anderson, K. A. +11 more
This paper presents an overview of a number of the principal findings regarding the hot plasmas ( E ≳ 50 keV) in Jupiter's magnetosphere by the HISCALE instrument during the encounter of the Ulysses spacecraft with the planet in February 1992. The hot plasma ion fluxes measured by HI-SCALE in the dayside magnetosphere are similar to those measured…
Chemical Composition of M8 Based on IUE and Visual Observations
Dufour, R. J.; Torres-Peimbert, S.; Peimbert, M.
We present optical and IUE observations of the Hourglass Nebula which is embedded in the galactic H II region M8. By comparing the intensities of the [C III] lines λλ1907 + 1909 with that of C II λ4267, a value of t2 = 0.046±0.01 is obtained. The logarithmic abundances by number of the gaseous component for t2 = 0.046 are: H …
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…