A SEARCH FOR VARIABLE-STARS IN THE GLOBULAR-CLUSTER M3

We describe here the results of a photometric time-sequence survey of the globular cluster M3 (NGC 5272), in a search for contact and detach ed eclipsing binary stars. We have discovered only one likely eclipsin g binary and one SX Phe-type star in spite of monitoring 4077 stars wi th V < 20.0 and observing 25 blue straggler stars (BSS), The newly ide ntified SX Phe star, V237, shows a light curve with a variable amplitu de. Variable V238 shows variability either with a period of 0.49 d or with a period of 0.25 d. On the cluster colour-magnitude diagram, the variable occupies a position a few hundredths of a magnitude to the bl ue of the base of the red giant branch. V238 is a likely descendant of a binary blue straggler. As a side result we obtained high-quality da ta for 42 of the previously known RR Lyrae variables, including 33 of Bailey type ab, seven type c and two double-mode pulsators, We used eq uations that relate the physical propel-ties of RRc stars to their pul sation periods and Fourier parameters in order to derive masses, lumin osities, temperatures and helium parameters for five of the RRc stars. We also tested equations that relate the [Fe/H], M-V and temperature of RRab stars to pulsation period and Fourier parameters. We derived [ Fe/H]= -1.42 in good agreement with spectroscopic determinations.