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Ultraviolet Study of U1341-CYGNI = CYGNUS-X-2 - Observations of an Accretion Disk
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +1 more
Observations of Cyg X-2 with the International Ultraviolet Explorer in the range 1200-3000 A are discussed with particular reference to the continuum. The dereddened UV spectrum indicates the presence of a contribution from a hot region of small area which is naturally interpreted as an X-ray heated accretion disk. Assuming an average X-ray lumino…
The spectra of two new intermediate helium stars.
Drilling, J. S.
The stars designated as LSS 2394 and LS II + 36 deg 37 in the Case-Hamburg Luminous Stars surveys are found to be intermediate helium stars. The environment and spectrum of LSS 2394 (CPD -62 2124) appear to be quite similar to those of Sigma Ori E in a number of respects, including close proximity to two other OB stars, membership in a rich O asso…
UV and optical observations of X-ray sources in the Magellanic Clouds.
Tanzi, E. G.; Tarenghi, M.; Hammerschlag-Hensberge, G. +7 more
Ultraviolet spectra of the Magellanic Cloud X-ray sources LMC X-4, SMC X-1 and SMC X-2 obtained by the IUE satellite are presented together with simultaneous optical photometry of SMC X-1 and SMC X-2. Short- and long-wavelength IUE spectra for LMC X-4 taken near X-ray eclipse provide no evidence for P Cygni-type emission, despite evidence for mass…
Is PKS 2155 an extragalactic source?
Maraschi, L.; Tanzi, E. G.; Tarenghi, M. +1 more
The X-ray source H2155-304, identified with the radio source PKS 2155 and with a 14 mag star-like object, is commonly believed to be a BL Lac object on the basis of the blue featureless continuum, the presence of optical polarization, and the violent variability (mB varies from 12.8 to 14.2 on a time scale of months). This paper present…
IUE high-dispersion spectrum of R Aqr.
Johnson, H. M.
Emission-line spectra of several ions were observed in R Aqr in the wavelength range 1900-3000 A. C II diagnostics gives an electron density of about 400,000/cu cm and an electron temperature of about 10,000 K. The Mg II doublet profiles are grossly asymmetric, of a P Cygni type with terminal ejection velocity of at least 200 km/s. This is like Mg…
History of the gamma-ray light curves of the pulsars PSR0531 plus 21 and PSR0833-45 as measured by COS-B
Caraveo, P. A.; Bignami, G. F.; Hermsen, W. +7 more
On the Evidence for High Energy γ -ray Emission from the Orion Nebula Stemming from COS-B Observations
Caraveo, P. A.
The E.S.A. COS-B satellite performed a one-month observation pointing in the direction of M42 in Orion, during July-August 1978. An excess of high energy (above 100 MeV) photons is seen in the data, well coinciding with the Orion cloud complex. Features of such an excess are discussed, such as flux value, spectral shape and possible spatial extens…
The transition region structure of kap Cet.
Rego, M.; Fernandez-Figueroa, M. J.; de Castro, E.
Ultraviolet emission lines of Kappa Ceti (HD 20630), obtained with the IUE satellite, are analyzed in order to study the higher chromospheric, transition region and the low corona structure. Three models are derived for the emission measurement distribution, and the best fit model has a pressure of log Pe equals 14.96 at log Te
Molecular hydrogen ion (H2+) absorption in planetary nebulae.
Feibelman, W. A.; Hobbs, R. W.; Boggess, A. +1 more
Several IUE spectra of planetary nebulae show an absorption feature shortward of 1500 A which is believed to be due to H2(+). The nebulae are excited by stars of spectral type O3-O7 or continuum, and all but one have double-shell structure.
UV observations of the intermediate helium star CPD -46 3093.
Heber, U.; Hunger, K.
UV spectrograms of CPD-46 deg 3093 have been obtained with IUE in low resolution. No evidence for mass loss can be found at this resolution. A synthetic spectrum, calculated in LTE and including 800 atomic transitions matches the observations. Also the UV Si III/Si IV ionization equilibrium is reproduced as well as the Stromgren colors. The atmosp…