Digitization of Astronegatives of the Pulkovo Glass Library: Positions of Saturn's Major Satellites in the Period 1972-1982 in the Gaia DR2 System

Abstract

We present the results of the re-reduction of Pulkovo photographic plates with images of Saturn's major satellites in the Gaia DR2 catalog system (169 plates, 3007 individual positions). Astronegatives were taken with the 26-inch refractor at the Pulkovo Observatory between 1972 and 1982. The intrinsic accuracy of measurement of astronegatives using the Pulkovo MDD system was 1 μm (20 mas on the 26-inch refractor scale). The mean values of O-C differences when compared with the most up-to-date ephemerides vary within ±20 mas. The errors of the annual mean differences are usually better than 20 mas. There is a close agreement between the presented Pulkovo series and the results of the re-reduction of similar USNO observations (mean seasonal differences are less than 50 mas in modulus). Considering that different implementations of modern ephemerides give satellite positions that vary within ±50 mas for the time interval under study, we can conclude that the Pulkovo series is highly informative for improving the motion models of the major satellites of Saturn.