WeCAPP -Wendelstein Calar Alto pixellensing project I^*

Tracing dark and bright matter in M 31

Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany

Corresponding author: A. Riffeser, arri@usm.uni-muenchen.de

Received: 12 April 2001
Accepted: 6 September 2001

Abstract

We present WeCAPP, a long term monitoring project searching for microlensing events towards M 31. Since 1997 the bulge of M 31 was monitored in two different wavebands with the Wendelstein 0.8 m telescope. In 1999 we extended our observations to the Calar Alto 1.23 m telescope. Observing simultaneously at these two sites we obtained a time coverage of 53% during the observability of M 31. To check thousands of frames for variability of unresolved sources, we used the optimal image subtraction method (OIS) by Alard & Lupton ([CITE]). This enabled us to minimize the residuals in the difference image analysis (DIA) and to detect variable sources with amplitudes at the photon noise level. Thus we can detect microlensing events with corresponding amplifications of red clump giants with M_I=0.