Published online by Cambridge University Press: 04 August 2017
The HIPPARCOS Star Mappers were designed to determine the satellite attitude by observation of stars with known positions. ESA has now enhanced them so that the continuous photon counts from two photo multipliers with B and V response will be recorded. The records will be used to derive an astrometric and photometric catalogue, the TYCHO Catalogue, complete to about B=11 mag and thus containing about 500 000 stars. The positions, annual proper motions and parallaxes will have an accuracy of about 0.03 arcsec and the magnitudes one of 0.03 mag.
The instrument is described and some aspects of the data reduction are discussed, namely the evaluation of a photon record by means of numerical filters, and the use of a TYCHO Input Catalogue.