Warsaw Variability Surveys

Four large/medium size photometric surveys are being conducted by Warsaw astronomers: Warsaw-LCO survey of globular clusters, OGLE, DIRECT and ASAS. In this contribution we provide short description of these projects and discuses briefly some results obtained for pulsating variables. 1. Warsaw-LCO survey of globular clusters The main goal of the survey is identification of detached eclipsing binaries in globular clusters. Such binaries can be used as excellent distance and age indicators (Paczyński 1997). Thirteen globular cluster were surveyed since 1993. Starting with 1997 most of the data are collected with the Las Campanas 1.0m Swope telescope equipped with SITe 2048 × 3150 CCD giving field of view 14.4 × 22.8 arcmin. Some additional follow-up observations are conducted on the 2.5m du Pont telescope. For a given cluster the total length of monitoring ranges from 30 to 150 hours with the median value around 70 hours. Precise and well sampled light curves of RR Lyr and SX Phe stars are collected as a side result of the survey. These data become available through Internet (http://sirius.astrouw.edu.pl/~kaluzny/) immediately after results for a given object are published. A list of monitored clusters and numbers of variables identified in them are given in Table 1. While monitoring M55 we identified five variables being likely members of the Sagittarius dwarf galaxy: two RRab stars and three SX Phe variables. 1.1. Non radial pulsators in M55 Our sample of pulsating variables from the globular cluster M55 includes five newly identified RRc stars. The light curves of three of these stars exhibit changes in amplitude of over 0.1 mag on the time scale shorter than a week. Detailed analysis indicates that observed changes are most probably due to non radial pulsations (Olech et al. 1999). At least 12 out of 24 SX Phe variables identified in M55 show a presence of two or more periodicities in their light curves. Table 2 lists principal periods, ratio P1/P2 and amplitudes for first terms of Fourier series calculated for both periods after appropriate pre-whitening was applied. The derived values of P1/P2 indicate that we are dealing with non radial pulsations. In Fig. 1