Gravitational microlensing and the Hamburg quasar monitoring program

Abstract

In May 1989 we started an extensive optical photometric monitoring program of quasars which are promising candidates for gravitational microlensing. We use the Calar Alto 1.2m telescope equipped with a CCD camera to obtain the quasar fluxes relative to stars included in the frames. The reduction is carried out immediately after the observation. Our main intention is to detect and analyse microlensing high amplification events. From the data obtained up to now, we find good evidence that quasars closely associated with foreground galaxies show a higher degree of variability than usual ones and interpret this result in terms of microlensing. There is, however, no evidence for a correlation between variability and the presence of strong heavy element absorption systems. In the first part of this contribution we give an overview on the basic microlensing theory and their applications to observed lightcurves. In the second part we discuss the monitoring program in some detail and present our first results.