Light curves and periods of Mira variables

Good distance indicators are needed in studies of the galactic structure. Pulsating variables can be used, but the problem is to find a homogenous sample obeying a period-luminosity relation with low scatter. In this paper, we show how such a sample can be produced using the Terzan catalogue of Variables and available Schmidt plates. We have selected 150 large amplitude variables discovered by Terzan in a held of 25 sq degrees near the Galactic Centre. A set of 22 red plates was scanned with the MAMA machine, providing time series for all the variables. The times series were analysed using both the periodogram and Renson's method. Periods could be derived for 122 stars of the sample showing clearly that most of these objects are Miras. As a conclusion we show that with some infrared photometry, these Miras could be used as good distance indicators in this region.