Search Publications
X-Ray and Optical Observations of X-Ray--selected BL Lacertae Objects
Maccagni, D.; Giommi, P.; Garilli, B. +4 more
Results from several X-ray and optical observations of five X-ray-selected BL Lacertae objects are reported. X-ray light curves covering periods of up to 6 yr reveal that the X-ray flux from these objects does not show large-amplitude trends over this time scale. Variations of up to 2 mag have been observed in the optical. The soft X-ray spectra o…
Spectral Synthesis in the Ultraviolet. I. Far-Ultraviolet Stellar Library
O'Connell, Robert W.; Thuan, Trinh X.; Fanelli, Michael N.
A library of mean stellar energy distributions for use in population synthesis of the ultraviolet spectra of active star-forming galaxies is derived from the ultraviolet spectrophotometry in the IUE Spectral Atlas. The spectra extend from 1230 to 1930 A with a resolution of 6 A. The library contains eight main-sequence groups from O3 to A7 V, four…
Ultraviolet Spectra of HH 1 and HH 2: Spatial Variations and the Continuum Problem
Raga, A. C.; Witt, A. N.; Brugel, E. W. +3 more
High-SNR 12-hr and 14-hr ultraviolet spectra of HH 1 and HH2 in the IUE short-wavelength range are reported. HH 1 data show a (spatial) half-width of the image size in the C IV 1548-A, 1551-A line which is smaller than the spatial half-width for the semiforbidden C II 1907-A, 1909-A line. A qualitatively similar situation is shown for HH 2, althou…
First Unambiguous X-Ray Detection of R Aquarii
Piro, L.; Friedjung, M.; Viotti, R. +1 more
The authors report coordinated ultraviolet and X-ray observations of the symbiotic Mira R Aqr obtained with IUE and EXOSAT in 1985 June and December at phases 0.0 and 0.5 of the Mira light curve. They have detected with the Low-Energy EXOSAT detector a weak X-ray flux of 5.4 and 4.6×10-3 counts s-1 at the two epochs, respecti…
Ultraviolet Spectra and Chromospheres of Cool Carbon Stars
Johnson, Hollis R.; Luttermoser, Donald G.
The authors assemble and discuss all available low-resolution IUE spectra of N-type carbon stars - including TW Hor, BL Ori, UU Aur, NP Pup, U Hya, T Ind, and TX Psc. Identification of spectral features is aided by a composite spectrum. Shortward of 2850 A only emission lines of C II, Mg II, Al II, and Fe II are seen, while the spectrum longward o…
The Problem of V444 Cygni
Underhill, A. B.; Fahey, R. P.
The authors have studied the changes of the spectrum of V444 Cygni (WN5+O6) shown on 13 high-resolution spectrograms obtained with the IUE. Evidence is found for an orbital-phase-dependent "third light" both in line and in continuum wavelengths. A model for the V444 Cygni system consisting of an O star with Teff = 40,000K, R/R_sun; = 10…
The Properties of Bursts with Short Recurrence Times from the Transient X-Ray Source EXO 0748-676
Haberl, Frank; Parmar, Arvind N.; White, Nick E. +1 more
On January 13/14 1986 Exosat performed a 11.3-hr observation of the transient X-ray burst source EXO 0748-676. The source was in a low state and emitted 11 type I X-ray bursts, of which 10 were analyzed in detail. The properties of the bursts were similar to those found in previous low-state observations reported in Gottwald et al. (1986). The tot…
The X-Ray Spectrum of Markarian 509 Observed by EXOSAT
Molteni, D.; Morini, M.; Lipani, N. A.
Mrk 509 was observed with Exosat at three different epochs during October and November 1983. Variability of about 30 percent was apparent both in the medium-energy (1-10 keV) and in the low-energy (less than 2 kev) X-ray bands between the different observations, on a time scale of 10 days. No correlation between the two energy bands was observed. …
The Ionization Structure of Planetary Nebulae. VII. New Observations of the Ring Nebula
Barker, Timothy
New optical spectrophotometric observations of emission-line intensities have been made in eight positions in the Ring Nebula corresponding to those observed previously with the Ultraviolet Explorer satellite; the total coverage is therefore 1400 to 7200 A. The intensities are in generally good agreement with those found previously in correspondin…
Ultraviolet and Visual Spectroscopy of DB White Dwarfs
Nelan, E. P.; Wegner, G.
Visual wavelength and IUE ultraviolet spectroscopy and model atmospheres of DB white dwarfs are reported. A search for spectral lines due to elements other than helium, and in particular carbon and hydrogen, was made. In no case is there a positive detection of carbon from these data, and upper limits relative to helium by number are derived in th…