Search Publications
Magnetically Controlled Circumstellar Matter in the Helium-strong Stars
Shore, Steven N.; Brown, Douglas N.
This paper reports the observation and interpretation of the ultraviolet spectrum variations of nine helium-strong stars: HD 36485, 37017, 37479, 37776, 58260, 60344, 64740, 96446, and 133518. A unified model is developed to account for the observed correlation among three stellar properties: the line profile characteristics of the C IV and Si IV …
A Study of the Baldwin Effect in the IUE Data Set
Koratkar, A. P.; Kinney, A. L.; Rivolo, A. R.
We have investigated the controversial relation between the continuum luminosity and the C IV λ1550 emission-line strength in the spectra of quasars, commonly referred to as the Baldwin Effect, as a possible indicator of absolute luminosity, We have used all available quasar spectra in the IUE archives which have C IV and/or Lyα shifted into the I…
Broad-Band Properties of the CfA Seyfert Galaxies. III. Ultraviolet Variability
Krolik, J. H.; Edelson, R. A.; Pike, G. F.
Six hundred fifty-seven archived IUE spectra are used to study the ultraviolet variability properties of the six members of the CfA Seyfert 1 galaxy sample with many repeated observations. All Show strong evidence for continuum and line variations. There is a tendency for less luminous objects to be more strongly variable. Most objects show a clea…
The ultra-compact broad emision line region in NGC 4151.
Perola, G. C.; Boksenberg, A.; Penston, M. V. +6 more
New observations of the UV continuum and emission lines of a Seyfert I galaxy are presented in which the time resolution is adequate to describe the character of variability. Using the IUE satellite, the nucleus of NGC 4151 was observed with a mean interval of 3.4 d during 2 months. The flux of the continuum and of most emission lines underwent la…
The Ultraviolet Calibration of the Hubble Space Telescope. IV. Absolute IUE Fluxes of Hubble Space Telescope Standard Stars
Bohlin, Ralph C.; Gry, Cecile; Holm, Albert V. +1 more
UV fluxes are presented for 37 stars selected as calibration standards for the Hubble Space Telescope (HST). In order to provide data of maximum precision, new absolute calibrations have been derived for the IUE SWP and LWR cameras for point sources in the large apertures, while the sensitivities of the trail and small aperture observing modes rel…
Optically Thin Thermal Emission as the Origin of the Big Bump in the Spectra of Active Galactic Nuclei
Peterson, B. M.; Korista, K. T.; Ferland, G. J.
The nature of the "big bump," the excess of ultraviolet emission seen in many active nuclei, is a clue to the source of the energy generation in the central regions of quasars. We report observations of the Seyfert galaxy Mrk 590, which show dramatic changes in both the continuum and hydrogen lines, thus offering a clue to the origin of the "big b…
The X-ray emission of 3C 273.
Koyama, K.; Nandra, K.; Tanaka, Y. +12 more
The X-ray emission of 3C273 in the 0.2-35 keV band has been studied, with EXOSAT and Ginga, over the period 1983 December to 1985 December. The overall flux is variable on a time-scale of weeks by a factor of 2. The spectral index in the 2-10 keV band (α ~0.5) is significantly different from the 'canonical' AGN index of α = 0.7. There are small bu…
Planetary nebulae with a high degree of ionization : NGC 2242 and NGC 4361.
Pena, M.; Torres-Peimbert, S.; Peimbert, M.
New observations in the 3400 - 7500 A range are presented for NGC 2242 and NGC 4361, and new IUE observations are presented for NGC 2242. The physical conditions and chemical composition for these nebulae are derived. The ionization structure of both PN are very similar, the PN are very optically thin to Lyman continuum photons, and more than 90 p…
Ultraviolet and Optical Variations in Active Galactic Nuclei: The Seyfert 1 Galaxy NGC 5548
Talavera, A.; Netzer, H.; Wamsteker, W. +8 more
We describe the results of a project to study the combined ultraviolet- optical spectrum of the Seyfert I galaxy NGC 5548 over the period 1978- 1986. Of the many spectrophotometric observations made with a typical resolution of 5-8 A, 11 epochs were simultaneous and nine cover the range from 1150 to 7000 A. The combined IUE and ground-based observ…
A model for the planetary nebula NGC 7027.
Middlemass, D.
Extensive photoionization modeling of NGC 7027 is presented using the most recent observations available. The effects of the differential extinction caused by the local dust cloud are considered and corrections are made to large-aperture line fluxes. Abundances are derived from a large number of collisionally excited and recombination emission lin…