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Radio-loud and radio-quiet quasars observed by EXOSAT.
Saxton, R. D.; Turner, M. J. L.; Stewart, G. C. +2 more
We present results from the spectral analysis of EXOSAT data on 31 quasars, 18 radio-loud and 13 radio-quiet. Simple power-law models with fixed (Galactic) absorption give acceptable fits to the spectra obtained in the 2-10 keV band. Using the results from these fits we have compared the distributions of spectral indices α for the radio-loud and r…
The Optical Variability of PKS 2155-304
Miller, H. R.; Carini, Michael T.
The BL Lacertae object, PKS 2155 - 304, has been photometrically monitored for the past decade (1979-1990). Optical variations have been observed on time scales ranging from several minutes to several years. The variations detected with time scales on the order of minutes are among the fastest optical variations detected for a BL Lacertae object. …
Properties of the Massive X-Ray Binary 4U 1700-37 = HD 153919
Corcoran, M. F.; Heap, S. R.
The system parameters for the massive X-ray binary 4U 1700 - 37 are reexamined in the light of modern spectroscopic theory and new UV and X-ray data. The system is composed of HD 153919, an O6f star having a stronger wind, and an accreting neutron star. Revised parameters for the Of component are derived which are in accord with the parameters of …
CNO Abundances and Temperature Fluctuations in the Orion Nebula
Dufour, Reginald J.; Hester, J. J.; Walter, Donald K.
The largest UV-optical data base to date of the Orion Nebula has been assembled, and the CNO abundances their distribution at a statistically significant number of positions to the north and west of the Trapezium and out to a distance of 5 arcmin has been examined. The forbidden O III temperature increases with distance from Theta1 Ori C while the…
Ultraviolet imaging of the Jovian aurora with the Hubble Space Telescope
Paresce, F.; Vidal-Madjar, A.; Dols, V. +2 more
We present here for the first time a Lyman-α image of the north polar region of Jupiter obtained with the Faint Object Camera (FOC) on board the Hubble Space Telescope a few hours after the encounter of the ULYSSES spacecraft with Jupiter. The presence of high latitude regions of enhanced emission is clearly observed. A comparison with the locatio…
Observations of R Coronae Borealis Stars in Decline: Empirical Arguments for Dust Formation near the Stellar Surface
Stanford, S. A.; Clayton, Geoffrey C.; Drilling, John S. +1 more
We present new IUE observations which monitor the spectroscopic evolution of RY Sgr through a deep decline. These data, along with other IUE, visible, and infrared observations of declines in RY Sgr, R CrB, and V854 Cen, are considered in an attempt to understand the dust formation process and the source of the narrow- and broad-line emission seen…
The TYCHO Input Catalogue. Cross- matching the Guide Star Catalog with the HIPPARCOS INCA Data Base.
Turon, C.; Didelon, P.; Egret, D. +2 more
A Tycho Input Catalogue of three million stars brighter than V = 12,1 has been produced for the needs of the Tycho data analysis. This catalog results from the cross-matching of a subset of the Hubble Space Telescope Guide Star Catalog with the Hipparcos INCA Data Base. The cross-matching procedure is explained and statistics about the magnitude d…
The extreme helium star BD -9 4395.
Heber, U.; Jeffery, C. S.
Simultaneous optical and UV spectroscopy is used to investigate both the photospheric variations and emission-line behavior of the extreme helium star BD-9 deg 4395. The photospheric parameters of the star are rederived from the optical spectra by the method of fine analysis, on the basis of up-to-date atomic data and new line-blanketed model atmo…
Iron Abundance in the Hot DA White Dwarfs Feige 24 and G191 B2B
Thorstensen, John R.; Bowyer, Stuart; Vennes, Stephane +2 more
Attention is given to model calculations of the far- and extreme-UV line spectra of highly ionized Fe species (Fe IV, Fe V, and Fe VI) for hot high-gravity H-rich stars. A spectral analysis of 31 hr of exposure of the DA white dwarf Feige 24 with IUE in the echelle mode reveals the presence of Fe with an abundance relative to H by number of (5-10)…
Solar wind Halo electrons from 1-4 AU
McComas, D. J.; Bame, S. J.; Phillips, J. L. +2 more
In this study we use observations from the Ulysses solar wind electron spectrometer to make a first examination of the evolution of the solar wind suprathermal or halo electron population as a function of heliocentric distance beyond 1 AU. Solar wind electron analyzers previously flown to distances >1 AU did not resolve the halo electron distri…