Search Publications
Hipparcos: First results of the photometric processing
Mignard, F.; Grenon, M.; Falin, J. L. +1 more
The analysis of the photon counts collected by the ESA HIPPARCOS satellite allows to determine for each program star a magnitude in the H-filter. We present the general principles of the data reduction restricted to the photometry. It is shown that photometric recognition of close binary stars, down to 100 arcsec separation is an attainable goal, …
Luminosity of large amplitude variable stars: Comparison between ground-based predictions and observations by the Hipparcos satellite
Barthes, D.; Mennessier, M. O.; Davies, P.
Since November 1989, the HIPPARCOS satellite has been observing stars in order to fulfil its mission goals. The complete data processing of these observations will take many years to perform. A small group of stars, namely the large amplitude variables, must be processed much closer to real-time so that the luminosity ephemeris can be updated wher…
Cometary ion distributions near the pickup energy outside comet Halley's bow shock
Coates, A. J.; Neugebauer, M.; Gombosi, T. I. +2 more
This paper compares calculated and measured energy spectra of implanted H+ and O+ ions on the assumption that the pick-up geometry is quasi-parallel and about 1% of the waves generated by the cometary pickup process propagates backward (towards the comet). The model provides a good description of the implanted O+ a…
EXOSAT observations of the iron line in CEN X-3
Fabian, A. C.; Tennant, A. F.; Takalo, L. O.
Properties of the iron line in Cen X-3 have been studied, using the gas scintillation proportional counter onboard EXOSAT. The iron line energy is seen to be constant (kT = 6.59 +/- 0.06 keV) over orbital and pulse periods. On the other hand the iron line intensity is seen to vary with both periods. The pulse period variations are sinusoidal, but …
Astronomy with EXOSAT
White, N. E.
The European Space Agency's X-ray observatory EXOSAT was operational from May 1983 to April 1986 and in that time made 1780 observations of a wide variety of objects including active galactic nuclei, stellar coronae, cataclysmic variables, white dwarfs, X-ray binaries, clusters of galaxies and supernova remnants. The 90hr high earth orbit allowed …
Time variability of stellar coronal sources observed by EXOSAT
Schmitt, J. H. M. M.; Pallavicini, R.
We present an overview of time variability in stellar coronal sources as observed with the EXOSAT satellite. We focus on M dwarf flare stars and we discuss both quiescent and flaring emission. We also outline recent developments in the modelling of stellar flares.
Temperatures of coronae of cool stars, derived from EXOSAT observations
Mewe, R.; Schrijver, C. J.; Lemen, J. R.
We observed the late-type stars Capella, σ2 CrB, λ And, AD Leo, GL494, GL569 and Procyon with different combinations of three instruments aboard EXOSAT : the low-energy channel multiplier array (LE), the medium-energy proportional counters (ME), and the transmission grating spectrometer (TGS). We derive crude temperature information on …
Current ideas about the production of the electroglow of Uranus
Clarke, J. T.
A process known as ``electroglow'' was identified by Broadfoot et al. /1/ shortly after the Voyager Uranus encounter as soft charged particle excitation of atmospheric gas in the presence of sunlight and in excess of the available photoelectron energy. Localized aurora and diffuse H and H2 band emissions have been observed from Uranus, …
Gamma rays and interstellar gas in the Cepheus region: A new gamma-ray source?
Grenier, I. A.; Lebrun, F.
A recent CO survey of the Cepheus Flare region (100°<=1<=141°, 8°<=b<=22°) has allowed a detailed study of the diffuse gamma-ray emission and the gas content of this nearby region. The comparison of the HI and CO observations with the COS-B gamma-ray data yields estimates of the N(H2)/WCO ratio in this molecular complex and …
First ultraviolet observations of the transition regions of X-ray bright solar-type stars in the Pleiades
Linsky, J. L.; Caillault, J. -P.; Vilhu, O.
Nearby clusters, such as Ursa Major, the Hyades, and the Pleiades, have been extensively studied in the X-ray regime. The first two clusters have also been studied with the IUE. However, the younger, fainter Pleiades cluster, which contains the youngest, and presumably most active, main sequence stars in the solar vicinity, had not been observed i…