Search Publications
Ultra low frequency waves at the magnetic pile-up boundary of comet P/Halley
Glassmeier, K. -H.; Belmont, G.; Rème, H. +2 more
Around the magnetic pile-up boundary observed by Giotto at 135,000 km from the nucleus of comet Halley, plasma and magnetic features display evidence of ultra-low frequency modes. Outside the pile-up region, a large region is characterized by an anti-correlation between the electron plasma density and the magnetic field strength. The study of the …
Giotto extended mission
Schwehm, Gerhard
The navigation of the ESA spacecraft Giotto to its encounter with comet P/Halley on 14 March 1986 required just 10% of the fuel available. Although the spacecraft was damaged by dust impacts during its close flyby at the nucleus of P/Halley it was retargeted to return close to Earth to maintain the option to extend the mission to encounter another…
Far ultraviolet spectrophotometry of BD +28 4211
Green, James C.; Cook, Timothy A.; Cash, Webster
We report the results of a November 1989 rocket flight which recorded a flux calibrated spectrum of BD +28 4211 from 912 to 1150Å with 1Å resolution. BD +28 4211, an SdO type star, is commonly used as an ultraviolet calibration source in the IUE wavelength band. Our work extends the useful range of this standard shortward of Lyman α. Since previou…
The variable energy-distribution of the gamma-ray emission from Geminga
Grenier, I. A.; Hermsen, W.; Hote, C.
The gamma-ray emission of Geminga during five COS-B observations has been analysed to derive its spectral properties between 50 MeV and 5 GeV. In all observations but one, the spectrum presents a turnover between 100 and 200 MeV, the source becoming very weak at the lowest gamma- ray energies. During the remaining observation, the spectrum is cons…
Plasma parameters near the comet Halley bow shock
Coates, A. J.; Neubauer, F. M.; Rème, H. +5 more
We analyse the available plasma data from the JPA, MAG and RPA instruments on Giotto for the inbound bow shock crossing at comet Halley. Proton, cometary heavy ion, electron and magnetic field data are combined on the inbound pass to yield the pressures of all the plasma components, and hence the characteristic plasma speeds and the Mach number of…
Astrometry using the hubble space telescope fine guidance sensors
Benedict, G. F.; Hemenway, P. D.; Jefferys, W. H. +2 more
The U. S. National Aeronautics and Space Administration in a cooperative effort with the European Space Agency has developed a large optical telescope with an aperture of 2.4 meters and a length of 8.8 meters. This instrument, the Hubble Space Telescope was launched by the space shuttle (STS-31) on the morning of 24 April 1990 and was placed in ea…
Ultraviolet observations of cataclysmic variables
Verbunt, Frank
The ultraviolet spectra of cataclysmic variables provide us with information on the mass transfer in these systems, and on the variations therein on different time scales. The combined ultraviolet and optical spectra cannot be fitted with simple model spectra, and accordingly, our interpretations of the observed spectra are subject to uncertainty.…
Scientific requirements for very accurate astrometry
Turon, C.; Kovalevsky, J.
Two types of accurate astrometric data are considered:
1) Survey astrometry providing absolute parallaxes and annual proper motions with an accuracy of 2 milli-arcsec, to a few tenth of a milli-arcsec. Parallax determinations will advance our basic knowledge of the Universe by giving the necessary strong foundations for the first steps of the…Hipparcos calibration
Schrijver, Hans
The methods and results of various Hipparcos in-flight calibrations are described. The geometrical calibrations allow the determination of the instrument distortions in the main field of view to better than a milli-arcsecond. A systematic decrease of the basic angle at a rate of two milli-arcseconds per month has been measured during the first 7 m…
A comparison between two strategies of data reduction for the Hipparcos project
Lattanzi, M. G.; Bucciarelli, B.; Sarasso, M. +2 more
Two different strategies for reducing HIPPARCOS data are directly compared and their respective impact on the final precision of the HIPPARCOS Catalog is evaluated. These strategies are the FAST (Fundamental Astronomy by Space Techniques) Consortium's Baseline and GLOBUS procedures. The Baseline is already operating on satellite data; GLOBUS was i…