PULSATION IN HIGH AMPLITUDE DELTA-SCT STARS

It has been pointed out by earlier authors that radial pulsation seems to be the only type present in high amplitude delta Set stars, at lea st for monoperiodic stars. In order to confirm this or not, we have co llected all the multicolor data available for these stars in the Strom gren and Johnson photometric systems. Then, the type of pulsation has been analysed on the basis of the phase shifts and amplitude ratios be tween observed light and colour variations. The results indicate that all the stars analysed, including both high amplitude delta Set (Popul ation I) and SX Phe (Population II) stars, are radial pulsators. This is also true for the monoperiodic medium amplitude delta Set stars ana lysed.