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Parallaxes and the Hertzsprung-Russell diagram for the preliminary HIPPARCOS solution H30
Grewing, M.; Evans, D. W.; Lindegren, L. +20 more
We outline the principles by which absolute trigonometric parallaxes have been derived from the first 30 months of data acquired by the Hipparcos astrometry satellite. Distributions of the parallaxes and formal errors of more than one hundred thousand stars are presented, indicating median standard errors of about 1.5milliarcsec (mas). Tests which…
Zero-point and external errors of HIPPARCOS parallaxes
Arenou, F.; Lindegren, L.; Turon, C. +4 more
A good knowledge of both accuracy and precision of the Hipparcos parallaxes is one of the keys for their future scientific use. For this purpose, the Hipparcos preliminary parallaxes, as obtained after the processing of the first 30 months of Hipparcos data, are compared to various ground-based parallax estimates, using astrometric, photometric an…
Linking the HIPPARCOS Catalogue to the extragalactic reference system.
Lindegren, L.; Kovalevsky, J.
We present an overview of the methods currently planned to link the Hipparcos reference system to the conventional extragalactic reference system, as defined by VLBI observations. The link programme consists of VLBI and connected element interferometry of radio stars, separation measurements with the Hubble Space Telescope, photographic observatio…
CCD photometry of the δ-Scuti star κ^2^ Bootis.
Kjeldsen, H.; Hjorth, J.; Thomsen, B. +4 more
CCD time-series differential photometry of the binary star κBoo has been carried out from a small in town situated telescope. One component of the system is known to be a δ-Scuti pulsator. Due to the high S/N data, four frequencies have been detected even though the window function is quite complicated. A search for a standard model that fits all …
Preliminary link of the HIPPARCOS and VLBI reference frames
Lindegren, L.; Mignard, F.; Lestrade, J. -F. +12 more
We present a comparison of VLBI and Hipparcos astrometric parameters of several optically bright radio-emitting stars. The systematic discrepancies found in these preliminary data can be removed by performing a single global rotation between the extragalactic and Hipparcos reference frames. Two estimates of this rotation and its time derivative ha…
Estimating the external accuracy of HIPPARCOS parallaxes by deconvolution.
Lindegren, L.
The external standard errors of a statistically homogeneous set of trigonometric parallaxes may be estimated from the distribution of small and negative parallax values. The paper describes a method using the Richardson-Lucy deconvolution algorithm combined with a fitting procedure to derive simultaneously an estimate of the distribution of true p…
New global solution of Earth orientation parameters from optical astrometry in 1900-1990.
Pesek, I.; Vondrak, J.; Ron, C. +1 more
Astrometrically observed variations of latitude and Universal time with thirty instruments of different types, located at 19 observatories all over the world, are used to derive polar motion, UT1-TAI (since 1956) and celestial pole offset at 5-day intervals. The values based on the observations of individual stars are used, the model of least-squa…
Construction of the intermediate HIPPARCOS astrometric catalogue
Lattanzi, M. G.; Lindegren, L.; Mignard, F. +15 more
The data analysis methods for the determination of the astrometric parameters from observations by the Hipparcos satellite as used in FAST and NDAC consortia for the construction of intermediate 18-month and 30-month solutions are presented. The quality of the results depends upon calibrations of the instrumental parameters, examples of which are …
Astrometry of double stars with HIPPARCOS
Badiali, M.; Cardini, D.; Emanuele, A. +13 more
After the processing of 30 months of the observations carried out by HIPPARCOS it is possible to provide reliable statistics on the number of double and multiple stars to be detected at the mission completion and on the quality of the astrometric and photometric results on these objects. About 21000 stars have been recognized as non-single, includ…
A comparison of ground-based stellar positions and proper motions with provisional HIPPARCOS results
Lattanzi, M. G.; Lindegren, L.; Mignard, F. +9 more
Preliminary positions and proper motions derived from the first 30 months of the Hipparcos mission are compared with some of the best ground-based catalogues and optical measurements. Comparison with FK5 and PPM very clearly brings out the zonal and regional errors of these catalogues. The proper motion system of PPM is found to have magnitude dep…