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From Interstellar Dust to Comets: A Unification of Observational Constraints
Greenberg, J. Mayo; Hage, J. I.
The interstellar dust model of comets is numerically worked out to satisfy simultaneously several basic constraints provided by observations of Comet Halley, and to derive the porosity of coma dust. The observational constraints are (1) the strengths of the 3.4 and 9.7 micron emission bands, (2) the shape of the 9.7 micron band, (3) the amount of …
Variability in the noise properties of Cygnus X-1.
Belloni, T.; Hasinger, G.
The aperiodic variability in the X-ray emission of Cyg X-1 is examined from 13 Exosat observations covering the period July 1983 - October 1985, by means of broad band 0.001-100 H3 power spectra. The total rms fractional variations in the range 0.016-14 Hz is between 28 and 38 percent. The power distribution is flat below a characteristic break fr…
Observations of Cygnus X-2 with IUE : ultraviolet results from a multiwavelength campaign.
Raymond, J. C.; Hasinger, G.; Verbunt, F. +3 more
IUE observations of Cyg X-2 obtained during June and October 1988 are reported and analyzed, with reference to data from simultaneous X-ray and radio observations and the predictions of theoretical models. The results are presented in extensive tables and graphs and characterized in detail. The UV flux is shown to increase monotonically as the X-r…
An atlas of aperiodic variability in HMXB.
Belloni, T.; Hasinger, G.
From EXOSAT archive data of 14 X-ray binaries (12 high mass X-ray binaries and 2 low mass X-ray binaries) broad band power spectra and color- color diagrams are produced. The aperiodic (noise) variability of the sources is studied. All the X-ray pulsars present in the sample show strong noise components in the emission, with a fractional variabili…
X-ray emission from solar neighbourhood flare stars : a comprehensivesurvey of EXOSAT results.
Tagliaferri, G.; Stella, L.; Pallavicini, R.
Exosat Observatory observations of flare stars pertaining to 25 separate sources are examined. The Exosat instrumentation is described, and a data sample is presented. Quiescent and flaring emissions from UV Ceti-type flare stars as observed with a low-energy experiment on Exosat are discussed, and the results of the timing analysis of the low-ene…
A Study of BL Lacertae--Type Objects with EXOSAT. I. Flux Correlations, Luminosity, Variability, and Spectral Variability
Maccagni, D.; Giommi, P.; Garilli, B. +2 more
Results are presented from a uniform and systematic analysis of more than 200 X-ray observations of 36 BL Lacertae objects obtained from the EXOSAT archive. All but two objects were detected at least once. Strong luminosity variability, which reached a factor of 30 in one case, was a common property of these objects. Variability was usually more p…
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…