A successful search for candidate RR Lyrae stars in four GCs of the Andromeda galaxy has been completed using HST archival data (Clementini et al. 2001b).
A reanalysis of the properties of RR Lyr's in the Sgr GC M 54 has been undertaken, using BVI photometric data obtained in 1999. The main results include the clear identification of multiple stellar populations in Sgr and the re-classification of M 54 as intermediate in the Oosterhoff groups, thanks to the improved photometric quality of our data and the much larger number of variable stars that could be detected. Fourier analysis of the light curves is presently being performed, in order to estimate the physical parameters of the variables.
The search for RR Lyrae variables was extended to the metal-rich GC NGC 6304 and the metal-poor Sgr cluster Arp 2. In both cases the sample of candidate variables has been more than doubled, and the characteristics of these stars have been derived. High quality BVI photometric observations were taken in November 2001 of the clusters NGC 362 and NGC 1904 for a detailed study of their RR Lyr's and the second-parameter effect.
A very detailed analysis of the RR Lyrae stars in M3 is presently being performed in collaboration with Corwin (Univ. of North Carolina). Mostly based on Fourier decomposition of the light curves, this study is showing the impact and characteristics of the Blazhko stars, the presence of a good number of evolved stars and their properties, as well as the characteristics of the main variable star population.