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EXOSAT observations of Cygnus X-1 : study of the soft X-ray excess.
Hasinger, G.; Balucinska, M.
The paper presents results of a spectral analysis of the Cyg X-1 data collected during 1984-1985 by the Medium Energy instrument onboard the Exosat satellite. Emphasis is on two issues: the soft X-ray excess in the range below 3 keV and the iron-line intensity. The presence of a soft component in addition to the high-energy power-law component is …
First Results from the Goddard High-Resolution Spectrograph: The Chromosphere of alpha Tauri
Ebbets, Dennis C.; Brown, Alexander; Walter, Frederick M. +5 more
The K5 III star Alpha Tau was observed with the Goddard High Resolution Spectrograph on November 27, 1990 as part of the Science Assessment Program for the HST. The spectra show intersystem and permitted chromospheric emission lines of semiforbidden C II and Si II, Fe II, Fe I, Ni II, and Co II. Resolved profiles of the semiforbidden C II lines in…
A Study of the Ultraviolet Evolution of U Geminorum between Outbursts
Szkody, Paula; Sion, Edward M.; Kiplinger, Alan L.
This paper examines the ultraviolet evolution of the dwarf nova U Gem from one outburst to the next. A series of seven sets of IUE observations that monitor the quiescent period of 22-103 days after outbursts is presented. An eighth set of observations obtained 75 days after the second outburst is included for comparison. In agreement with earlier…
Two early-type POST AGB stars at high galactic latitudes.
Dufton, P. L.; Keenan, F. P.; Conlon, E. S. +1 more
Two high galactic latitude B-type stars, PHL 1580 and PHL 174, originally identified as distant early-type objects from low-resolution spectroscopy and photometry are re-analyzed using high-resolution spectra. The results of LTE and non-LTE model atmosphere analyses reveal general metal underabundances relative to solar values of typically 0.6 and…
PW Vulpeculae: A Nova with Nearly Solar Abundances
Williams, Robert E.; Truran, James W.; Ferland, Gary J. +6 more
Optical spectrophotometry of PW Vulpeculae is combined with ultraviolet data to estimate electron temperatures, densities, and abundances in the ejecta of this slow classical nova. The reddening, the distance, and the evolution of the ultraviolet spectrum are discussed. Abundances are nearly solar, with the exception of nitrogen, which is substant…
The Local Interstellar Medium toward the Center of Loop I
Vladilo, Giovanni; Centurion, Miriam
The present study of the local insterstellar medium toward the center of Loop I analyzes optical and UV spectra of nearby stars within the l = 310-330 deg, b = 15-25 deg area. The analysis of the UV spectra reveals a sudden gas-column density increase as a function of distance from 10 to the 18th to 10 to the 20th/sq cm, suggesting the presence of…
NLTE-analysis of sublimous O stars : KS 292.
Rauch, T.; Werner, K.; Heber, U. +2 more
High-resolution spectra of the southern Galactic sdO star KS 292 are analyzed using modern NLTE model atmospheres in order to determine the atmospheric parameters. The results indicate that KS 292 probably belongs to a newly discovered group of post-AGB stars which are characterized by effective temperatures and gravities typical for central stars…
Faint Object Spectrograph Spectroscopy of Resolved Structure in the Nucleus of NGC 1068
Ford, H. C.; Kriss, G. A.; Armus, L. +7 more
We report the results of FOS spectroscopy of the continuum peak of NGC 1068 in the wavelength range 2200-7000 A. Detailed analysis reveals the emission lines to be complex in shape and to consist of a number of different velocity components. Both the Balmer lines and the strong forbidden lines have a contribution from a component with full width a…
The Orbital Ephemeris and Eclipse Transitions of the Low-Mass X-Ray Binary EXO 0748-676
Parmar, A. N.; Verbunt, F.; Corbet, R. H. D. +1 more
Using the eclipses as fiducial markers, an updated ephemeris for EXO 0748 - 676 is derived and evidence is found that between February 1985 and March 1989 the 3.82-h orbital period of EXO 0748 - 676 decreased with a time scale of -5 x 10 to the 6th yr. The sense of this change is the same as that predicted by simple models for the evolution of low…
Multiwavelength Observations of Nova LMC 1990 Number 2: The First Extragalactic Recurrent Nova
Williams, R. E.; Shore, Steven N.; Sonneborn, George +4 more
We present IUE and optical observations of Nova LMC 1990 Number 2, the first recurrent nova to be observed outside the Milky Way. The earlier optical outburst of the nova was observed in 1968, when it reached a maximum of about V = 10.9. IUE spectra were obtained between 1990 February 16 and March 26, with 8 hr resolution during the first day of o…