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Digitization, Data Reduction and Catalogues

The area chosen for digitization, data reduction and interpretation covers 216 plates, more than 30 % of the survey. It encompasses almost 5000 square degrees of the sky between declinations -17š.5 and -87š.5 and right ascensions 20^h30^m to 5^h30^m. Outside this area, star densities become too high for proper automatic detection and evaluation of single objects. 1.5 years were invested for scanning and basic reductions. The step size of 15 µ m and the aperture of 20 µ m * 20 µ m yield a positional accuracy of 0".3''. Due to the double slit and the high density range of our amplifier - its effective limit is determined by photon statistics rather than by sensitivity - we are able to measure system magnitudes in the range 14 <= m <= 21, with an accuracy of about 0^m.1 in the middle range and 0^m.2 in the very bright and very faint ranges. For magnitude corrections on individual plates (center-edge sensitivity variations) and for the determination of the catalogue zero points, standard sequences are being measured with the Dutch 0.90m telescope at La Silla and, in collaboration with Walter Wargau, University of South Africa, Pretoria, with the 1.0m telescope of the South African Astronomical Observatory (SAAO).

The galaxy catalogue lists 7.1 million galaxies down to magnitude m = 21, the star catalogue almost 20 million stars to the same limit. The catalogues will literally broaden - and hopefully deepen - our views in observational cosmology as well as in stellar statistics.


Michael.Naumann@eso.org