Search Publications
Correlation between variability time scale and X-ray spectral index in AGN.
Wilms, J.; Staubert, R.; Koenig, M.
We have analysed EXOSAT ME X-ray light curves of a sample of AGN assuming a stochastic process in these sources. The result is a significant anti-correlation between the relaxation timescale τ, derived from this stochastic model fit, and the photon index {GAMMA} of the X-ray spectrum. This establishes for the first time a relationship between vari…
On the interpretation of the extinction curves of R Coronae Borealis stars
Zubko, V. G.
The available extinction curves for some RCB stars (R CrB, RY Sgr, MV Sgr and V348 Sgr) have been analysed, making use of the method of regularization for solution of ill-posed problems. This approach allows an estimate of dust grain sizes responsible for fadings of RCB stars. A model involving graphite grains is shown to be preferable for the exp…
Timing the eclipse of HD185510
Simon, Theodore; Jeffery, C. Simon
HD185510 (=V1379 Aql) is an eclipsing double-lined RS CVn binary containing a K0 III/IV giant and a hot subluminous companion. An International Ultraviolet Explorer (IUE) ultraviolet light curve has been obtained through the eclipse of the companion with an average time resolution of one measurement every 19min. This was sufficient to resolve all …
Properties of hydromagnetic waves in the polar caps: ulysses
Forsyth, R.; Balogh, A.; Tsurutani, B. T. +3 more
Properties of the large amplitude Alfvén waves which are a dominant feature of the high latitude solar wind have been studied during the pole-to-pole passage of Ulysses. In addition, an effort has begun to identify magnetosonic waves at high latitude in spite of their expected small amplitude and the presence of the large amplitude Alfvén waves. T…
Alfvénic fluctuations in fast and slow solar winds
Orlando, S.; Peres, G.; Rosner, R. +1 more
We compute properties of Alfvénic fluctuations within a wide frequency range (i.e., 10-6s-1<~f<~10-2s-1) in both high- and low-speed magnetized radial solar winds. In particular, the radial and frequency variations of the normalized cross helicity σc, the Alfvén ratio <script>R<…
Ultraviolet variability of the Seyfert 1 galaxy Fairall 9
Clavel, J.; Rodriguez-Pascual, P. M.; Wamsteker, W. +5 more
The large amplitude of the variations of the Seyfert I Galaxy Fairall-9 between 1978 and 1991 make this Active Galaxy especially suitable for a combined study in terms of reverberation analysis and photoionization modeling over the velocity field of the broad lines of its ultraviolet spectrum. We have combined our ultraviolet data with those avail…
The Ultraviolet Extinction Curve for Circumstellar Dust Formed in the Hydrogen-Poor Environment of V348 Sagittarii
Clayton, Geoffrey C.; Drilling, John S.; Hecht, James H. +3 more
New International Ultraviolet Explorer (IUE) spectra with high signal-to-noise ratios have been obtained during the recovery of the hot R Coronae Borealis star, V348 Sgr, from its 1992 minimum. These spectra have been combined with spectra from the IUE archives to obtain a definitive extinction curve for dust recently ejected from this star, and m…
Contemporaneous IUE, EUVE, and High-Energy Observations of 3C 273
Kafatos, M.; Bruhweiler, F. C.; McHardy, I. M. +5 more
We present the results of our 1994 January and 1995 January observations of the quasar 3C 273 obtained with the International Ultraviolet Explorer (IUE) and the Extreme-Ultraviolet Explorer (EUVE). These observations were part of a large multiwavelength campaign to observe 3C 273 from radio through γ-rays. Our 1995 January photometric observations…
Detection of β Pictoris-like Gaseous Infall in 2 Andromedae
Neff, James E.; Cheng, K. -P.; Bruhweiler, Fred C.
Ultraviolet observations of 2 Andromedae with the Goddard High Resolution Spectrograph on board the Hubble Space Telescope (HST) clearly reveal the existence of circumstellar gas, in addition to previously known anomalous interstellar features, in the line of sight toward this nearby star. We also detect varying, redshifted Ca II absorptions, whic…
Cosmic ray modulation in a non-spherical heliosphere during solar minimum conditions
Potgieter, M. S.; Haasbroek, L. J.
It is expected that the position of the modulation boundary in the equatorial and polar regions of the heliosphere depends on solar activity and possibly also on the polarity of the heliospheric magnetic field. In general, it can be assumed that the changing outward solar wind pressure causes a dynamic boundary position. Since the solar wind plasm…