A Ground-Based Network of Observers for a Gaia Follow-Up

During the Gaia mission, beyond the 3-D cartography of the Galaxy, we hope to get the detection of several transient events. In order to be able to exploit these detections and to perform further studies of these events, a groundbased network of telescopes would be very efficient. Among the most common transient events, Gaia will probably detect a large number of new Solar System objects. Several among these objects will be fast moving objects, such as the Near Earth Objects and probably comets. A dedicated ground-based network will insure avoiding the loss of these objects. Besides the astrometric parameters, ground-based observations will also allow us to quickly characterize several physical properties such as their photometric variability which is of interest for the identification of these objects in further measurements by Gaia. This paper reports on some observational requirements for this follow-up programme and on the first attempts to build such a network