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H1504+65: an Extraordinarily Hot Compact Star Devoid of Hydrogen and Helium
White, N. E.; Giommi, Paolo; Holberg, J. B. +4 more
The optical identification of the bright soft X-ray source H 1504 + 65, originally discovered by the HEAO I A-2 low energy detectors, is reported. The optical counterpart exhibits a steep, virtually featureless continuum from optical wavelengths through the ultraviolet. The spectrum is remarkably featureless except for a broad O VI adsorption feat…
C +2 Electron Temperatures in Planetary Nebulae
Kaler, J. B.
Electron temperatures are calculated for 30 planetary nebulae from the flux ratios of the C III] λ1909 and C II λ4267 lines, both of which are produced in the C+2 zone of the nebula. These temperatures correlate much better with optical [O III] temperatures than they do with those derived from [N II], except for low central star tempera…
The Ultraviolet Calibration of the Hubble Space Telescope. I. Secondary Standards of Absolute Ultraviolet Flux and the Recalibration of IUE
Bohlin, R. C.
Spectral energy distributions of IUE standards are presented. The five UV standards, HD 60753, BD +75°325, HD 93521, BD +33°2642, and BD +28°4211, were well observed in the original calibration epoch of the IUE observatory and have been monitored for UV variability since the IUE launch in 1978. Only observations from the first year of IUE were use…
X-Ray Variability of the BL Lacertae Object PKS 2155-304 in the 0.1--6 keV Range
Maccagni, D.; Maraschi, L.; Tanzi, E. G. +5 more
Observations of the bright BL Lac object PKS 2155 - 304 obtained at 1-6 keV using the ME argon counters and channel-multiplier array at the focus of the Exosat LE telescope, in conjunction with the 0.05-2-keV-bandpass 3000-A Lexan filter, during a total of 30 h in October-November 1983 and November 1984 are reported. The data are presented in tabl…
The Behavior of the C IV Emission Line in Active Galactic Nuclei
Colina, L.; Wamsteker, W.
The behavior of the C IV 1550 A emission line strength in variable active galactic nuclei (AGNs) such as Seyfert 1 galaxies and one broad-line radio galaxy (BLRG) is discussed on the basis of low-resolution spectra from IUE. The results are compared with those obtained previously for QSO samples. The variation of individual AGNs indicate that they…
The Stellar Population of NGC 6166
Gregg, M. D.; Bertola, F.; Oemler, A., Jr. +1 more
New optical and ultraviolet observations were obtained of NGC 6166, a cD galaxy and strong radio source in which both a large cooling flow and ongoing star formation have been detected. The spectrophotometry has been analyzed by a technique of differential spectral synthesis, in which the galaxy spectrum is compared with a spectral sequence compos…
X-Ray Spectral Observations of the Crab-like Supernova Remnants G21.5-0.9 and 3C 58
Becker, R. H.; Smith, A.; Davelaar, J.
Broad-band (2 - 10 keV) spectral data of the Crab-like supernova remnants 3C 58 and G21.5-0.9 have been obtained from the medium-energy instrument on EXOSAT. Both objects show a simple power-law spectrum with a spectral index of 0.72±0.12 for G21.5-0.9 and 1.30±0.26 for 3C 58. VLA 21 cm absorption measurements for G21.5-0.9 indicate a distance of …
High-Dispersion Observations of Alpha Bootis (K1 III) with the International Ultraviolet Explorer
Jordan, C.; Linsky, J. L.; Brown, A. +2 more
The authors have obtained very deeply exposed IUE echelle spectrograms of the bright, early-K giant Arcturus. They did not detect significant flux in the most prominent high-excitation species of a solar-like transition zone, C IV λ1548.2. The presence of a weak feature of Si III] λ1892.0, and possibly also Si IV λ1393.8, indicates the existence o…
On the Ultraviolet Spectra of Type I Supernovae
Branch, D.; Venkatakrishna, K. L.
A synthetic-spectrum technique, applied previously to the interpretation of the optical spectra of Type I supernovae, has been extended to the maximum-light near-ultraviolet spectrum. Spectral features in the interval 2750-3450 A are suggested to be complex blends of overlapping P Cygni profiles produced by numerous Fe II and Co II lines. This int…
Variability of the BL Lacertae Objects PKS 2155-304 and OJ 287 in the Far-Ultraviolet
Maraschi, L.; Tanzi, E. G.; Tagliaferri, G. +1 more
All the ultraviolet spectra of the two bright BL Lacertae objects PKS 2155 - 304 and OJ 287 taken with the International Ultraviolet Explorer in the period 1978-1984 are examined. For each spectrum the best-fitting power law is determined and a correlation between spectral slope and intensity is searched for. The correlation, if present, is weak. …