The Hamburg quasar monitoring program at Calar Alto: Analyses of micro-lensing variability

Abstract

In May 1989 we started an extensive monitoring program in order to find and analyse micro-lensing events in the light curves of a selected sample of quasars. We use the MaxPlanck-Institute 1.23 m telescope at the German-Spanish Astronomical Centre on Calar Alto equipped with a CCD camera. For our program, 15-30% of the observation time at this telescope are available in the next five years. Fluxes are measured through different standard broad-band filters relative to comparision stars in the CCD frame. A 0.01 mug accuracy (in relative photometry) can therefore also be reached for non-photometric conditions. Standard CCD reduction, identification of the objects and photometry are carried out in about 5 rain immediately after each observation by using an automatic routine (on a MicroVAX 3200 workstation) developed by us. We want to obtain up to 30 data points for each objects annual observing period with a maximum spacing of two to three weeks. It is therefore possible to recognize a micro-lensing high amplification event (HAE) at its steep wing, assuming that the transverse velocity of the foreground stars relative to the line of sight to the quasar does not exceed 1000 km/s. Since it is supposed that some 'blazars' have radiation components with relativistic transverse velocities, some members of this class will be monitored with correspondingly higher time resolution during shorter periods. When a HAE or another interesting feature will be detected, the fast reduction allows us to follow the light curve with higher accuracy and by using more different filters.