TYCHO assessment

The photon counts from the HIPPARCOS star mapper contains significant photometric and astrometric information on at least 400 000 stars in the interval of magnitudes from B=2 to 11. Analysis of the first few weeks of data from this TYCHO experiment on-board the HIPPARCOS satellite has shown that the original expectations can be fulfilled with the revised mission during 3 years in the elliptical orbit. The software architecture described before launch is unaltered, but certain features have been streamlined and improved in accordance with the revised mission. The software for detection and estimation of the stellar flux has been improved so that the background is more accurately determined, and the disturbance from 'side lobes' and from 'spikes' is decreased. This, in connection with an observed 20 per cent higher detection efficiency and a 50 per cent lower background compensates for the 50 per cent loss of effective observing time in the elliptical orbit.