Search Publications
Geometrical stability and evolution of the HIPPARCOS telescope
Lindegren, L.; Le Poole, R. S.; Perryman, M. A. C. +1 more
A simple geometrical model of the Hipparcos telescope is described whereby the relative positions and orientations of critical optical elements can be derived from the field-to-grid transformation determined as part of the normal data processing. The instrument is very stable on time scales of hours, but secular drifts of the order of 0.1 micron/d…
Fe II Fluorescence and Anomalous C IV Doublet Intensities in Symbiotic Novae
Kafatos, M.; Michalitsianos, A. G.; Meier, S. R.
The variation of absolute intensities of Bowen-excited Fe II emission in the symbiotic stars RR Tel, RX Pup, and AG Peg is examined. The C IV doublet intensity ratios in RR Tel were not anomalous between 1979 and 1989, and the ratio had typical values within the optically thin range. The intensity of individual Fe II Bowen-excited lines is correla…
Electron distributions upstream of the comet Halley bow shock: Evidence for adiabatic heating
Anderson, K. A.; Neubauer, F. M.; Glassmeier, K. H. +4 more
We report on three-dimensional plasma electron (22 eV to 30 keV) observations upstream of the comet Halley bow shock, obtained by the RPA-1 COPERNIC (Rème Plasma Analyzer-Complete Positive Ion, Electron and Ram Negative Ion Measurements near Comet Halley) experiment on the Giotto spacecraft. Besides electron distributions typical of the undisturbe…
The spectrum of the VV Cephei star KQ Puppis (Boss 1985). III. A possible model.
Altamore, A.; Rossi, C.; Baratta, G. B. +2 more
Following a previous study by Altamore et al. of the ultraviolet spectrum of KQ Pup, and the spectral Atlas of this star by Altamore et al., the authors analyze coudé and CAT CES optical spectra of the object observed during 1969-1984, and compare with IUE data obtained in 1979. The ultraviolet to infrared energy distribution appears bimodal with …
Geometrical calibration and assessment of the stability of the HIPPARCOS payload
Schrijver, Hans; van der Marel, Hans
The various geometrical calibrations of the Hipparcos telescope and detection system are described. It is shown that these calibrations can be executed with the required precision of better than a milli-arcsecond. Moreover, it is shown that variations in the parameters describing the calibration results are very slow, yielding the picture of a ver…
X-Ray Continuum and Line Emission of the Seyfert Galaxy MCG-5-23-16
Singh, K. P.; Rao, A. R.; Vahia, M. N.
We report observations of X-ray continuum and line emission from the highly absorbed and variable Seyfert galaxy MCG -5-23-16, using the low- energy and the medium-energy detectors of the EXOSAT Observatory. The galaxy was observed in 1983 December and in 1984 May. The X-ray intensity of the source is observed to vary by ~25% in the hard (2-10 keV…
Attitude determination in the HIPPARCOS revised mission
Donati, F.; Falin, J. L.; Kovalevsky, J. +2 more
An accurate knowledge of the attitude as determined by the observation of star transits through the star mapper is an essential factor in the final accuracy of the Hipparcos reductions. In comparison with the nominal mission, several features tend to degrade the precision of the attitude determination: an irregular increase of the background noise…
Resolution of the southern radio lobe of 3C 33 at 660 NM
Stiavelli, Massimo; Crane, Phillipe
An HST planetary camera image of the southern radio lobe of 3C 33 has revealed a strand of emission coincident with the peak in the radio emission at 2 and 6 cm. The detailed morphological similarity between the optical and radio data confirms beyond doubt the common origin of the radio and optical emission, and raises the question of the physical…
Properties of fast winds in hot stars in the Magellanic Clouds.
Patriarchi, P.; Perinotto, M.
The early-type stars in the Magellanic Clouds for which good quality high-resolution spectra with the IUE satellite exist have been studied for their stellar wind. Their P Cygni profiles in the N V, C IV, Si IV, O V, and N IV lines have been investigated with the SEI (Sobolev plus exact integration) method. Particularly good fits of the theoretica…
Ion-cyclotron waves at Jupiter: Possibility of detection by Ulysses
Horne, Richard B.; Thorne, Richard M.; Mei, Yi
We evaluate the convective growth of ion-cyclotron waves in the Io plasma torus using realistic plasma parameters. Significant wave amplification is restricted to two dominant frequency bands. As originally proposed by Thorne and Moses [1983,1985], waves between the O+ and H+ gyro-frequencies may be excited at higher latitude…