Global reduction with proper motions for meridian observations

When we deal with astrometric observations spread over periods longer than a few years, it is of major importance to take into consideration the proper motions of all objects involved in the reduction process. Not to consider such quantities, mainly when they are poorly known to the majority of the objects, may significantly degrade the final results of the reduction. In this paper, we present a way to treat this problem. As an example, we reduced a set of over 170 000 observations made with the Bordeaux photoelectric automatic meridian circle, collected during almost ten years of work of the instrument. In our reduction model, proper motions were included as unknowns, along with positions and instrumental parameters. The method shown here, which we call global technique, is an extension of the overlap method introduced by Eichhorn (Eichhorn 1960), which was developed by many authors afterwards.