fitting software written by Ch.Alard for the DENIS project. A description of this code can be found in Schuller et al.([@Schuller03]). For the photometric calibration of the CTIO data we used standard stars from Landolt’s field RU149 (Landolt [@Landolt92]). Photometric accuracy of the resulting light curves could be analyzed by comparing measurements of variables in overlapping parts of the CTIO mosaic. Typical deviations were of the order of 0.007mag. We then used about 40 non-variable cluster stars ranging in $V-I$ between 0.9 and 2.1 to link the Mount Stromlo measurements to those from CTIO. Typical errors in the Mount Stromlo magnitudes were of the order of 0.013mag.

For various reasons (field of view, pixel scale, damaged parts of the CCD, depth of the observation) not all variables could be measured on both the CTIO and the Mount Stromlo data. In these cases only one of the data sets could be used for the analysis.

Our aim was to detect and measure long period variables on the upper part of the giant branch only. Thus we selected for analysis only those variables that varied on time scales of more than approximately 30 days with a total light amplitude of at least 