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The soft X-ray variability of NGC 5548.
Kaastra, J. S.
The soft X-ray variability of NGC 5548 is studied using EXOSAT's low energy telescope in conjunction with the channel multiplyer array (CMA). For the first time, the pulse height distribution of the CMA data is used to infer information on the spectral variability. The spectrum of NGC 5548 consists of a hard power law and a soft component. During …
The anomalous cases in the double star data reductions of the Hipparcos mission
Pannunzio, R.
In the present paper, some cases of objects observed by HIPPARCOS and whose signal is ``anomalous'' are considered. In this context, only the double stars giving wrong parameters during the automatic reduction chain, have been considered as ``anomalous''. For each case examined, a new mathematical model has been taken into account and inserted in …
A Cool Giant with a Circumstellar Cloud
Kondo, Y.; Gurzadian, G. A.; Perez, Mario R. +2 more
The IUE spectrum of the star HD 139521, a giant of class G8III is obtained and based on the analysis of the narrow structure of 2795 (k) and 2803 (h) MgII emission profiles, the existence of a circumstellar cloud around the giant star is assumed. This conclusion is confirmed also by the anomaly of the small observed power of the doublet MgII emiss…
The HIPPARCOS Input Catalogue - a Progress Report from an Astrometric Point of View
Turon, C.; Requieme, Y.
The construction of the Hipparcos satellite is proceeding according to the schedule and should be finished in March 1988. But, due to some problems with the Ariane European booster, the launch has now been postponed until 1989. In practice, this means that the astronomical community may expect delivery of the final Hipparcos Catalog only in 1995. …
VLBI astrometry and the Hipparcos link to the extragalactic reference frame
Lestrade, J. -F.; Preston, R. A.; Gabuzda, D. C. +1 more
The link between the optical and VLBI extragalactic reference frames is undertaken with a long-term program of differential VLBI astrometric observations of 12 radio stars. The status of the program and an assessment of the astrometric accuracy of these observations are presented.
The IERS extragalactic Celestial Reference Frame and its tie with HIPPARCOS.
Lestrade, J. -F.; Arias, E. F.; Feissel, M.
This Technical Note gives a presentation of analyses of VLBI extragalactic reference frames performed in the framework of IERS, in the course of the maintenance of its conventional celestial frame. In section 1 the definition of the IERS celestial reference system and its relationship with the 1991 IAU Resolution A4 on Reference Systems are descri…
Results of the HIPPARCOS in-orbit payload calibration.
Davies, P. E.; McDonald, A. J. C.
The HIPPARCOS satellite is the European Space Agency's first mission dedicated to global astrometry. The spacecraft is in a geostationary transfer-type orbit with perigee at about 500 km instead of the planned geostationary orbit. From this orbit, the satellite will systematically scan the entire sky using a predefined attitude law. The output of …
Double star CCD astrometry and photometry
Irwin, M. J.; Argue, A. N.; Lampens, P.
About 3000 CCD measurements of double stars have been made in one or both filters V and R on the 1m Jacobus Kapteyn Telescope at La Palma. The stars form part of the INput CAtalogue (INCA) of the astrometric satellite HIPPARCOS, and require both astrometry and photometry in order to facilitate reduction of the HIPPARCOS measurements. The primary c…
A Note on the Statistical Evaluation of Compressed Mass Spectra Obtained from Dust Particles in the Coma of Comet Halley
Jessberger, E. K.; Fomenkova, M.; Mukhin, L. +4 more
A weighing factor for individual dust grains based on an independent determination of the particle mass (rather than summing up the total number of ions of an element measured in all spectra) is established for the calculation of the average dust composition. The ion ratio distribution obtained from particles with different masses independent of c…
Améliorations des positions des etoiles Hipparcos par l'utilisation des observations ``star-mapper''
Mignard, F.; Donati, F.; Falin, J. L. +2 more
Results on star-mapper data for attitude determination based on observations carried out over fifteen reference great circle's (RGC) are presented and discussed. Precision on the three-angle attitude reconstruction is of the order of 60 milli-arcsec along-scan and 100 and 180 milli-arcsec normal-to-scan. With this first year data, it is possible t…