Search Publications
The continuum radiation of the symbiotic star AG Draconis in quiescence and during outbursts.
Leibowitz, E. M.; Formiggini, L.
Results of spectroscopic measurements of the continuum radiation of the symbiotic star AG Dra in the UV and optical regions are presented. The observations extend over a period of eight years and cover the quiescent state of the star as well as three outbursts which occurred during those years. The results suggest that outbursts of AG Dra are trig…
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…
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…
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…
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…
Multiwavelength observations of the quasar Q 1821+643 during the ROSAT All Sky Survey.
Malkan, M. A.; Ulrich, M. -H.; Heidt, J. +4 more
Temporal variations of the flux in the optical, UV, soft X-ray and medium X-ray ranges occur in most AGN studied, but no general correlation has emerged between the variations in these different energy ranges. Because of its high ecliptic latitude the radio-quiet quasar Q 1821 + 643 was surveyed for 37 days by ROSAT during the ROSAT All Sky Survey…
Modelling the torques affecting the HIPPARCOS satellite
Perryman, M. A. C.; van Leeuwen, Floor; Penston, Margaret J. +2 more
A description of the models used to derive a model of the torques working on the Hipparcos satellite and results based on 12 weeks of data spread over 14 months are presented. Most of the prelaunch estimates of the satellite's solar radiation torques is confirmed qualitatively. A reconstruction of the torques near apogee to a level of a few microa…
TYCHO background determination and monitoring
Wicenec, A.; Baessgen, G.
Attention is given to the method of background determination in the Tycho photon counts. A part of the data from the first eight months is used to study the periodical and aperiodical behavior of the background and provide statistics on the usability of Tycho data. The scientific value of the Tycho mission is directly correlated to the amount of l…
An extremely active giant star : HD 218153.
Simon, T.; Mayor, M.; Renan de Medeiros, J.
We report Coravel and lUE observations for the bright giant HD 218153, KU Peg. This star seems to be a spectroscopic binary with a period of about 1400 days. From the lUE spectrum we find that HD 218153 is among the most chromospherically active stars known up to this date.