A NEW APPROACH TO THE REDUCTION OF CARTE DU CIEL PLATES

A new procedure for the reduction of ''Carte du Ciel'' plates is prese nted. A typical ''Carte du Ciel'' plate corresponding to the Bordeaux zone has been taken as an example. It shows triple exposures for each object and the modeling of the data has been performed by means of a n on-linear least squares fitting of the sum of three bivariate Gaussian distributions. A number of solutions for the problems present in this kind of plates (optical aberrations, adjacency photographic effects, presence of grid lines, emulsion saturation) have been investigated. A n internal accuracy of 0.'' 1 in x and y was obtained for the position of each of the individual exposures. The external reduction to a cata logue led to results with an accuracy of 0.'' 16 in x and 0.'' 13 in y for the mean position of the three exposures. A photometric calibrati on has also been performed and magnitudes were determined with an accu racy of 0.(m)09.