Pulsation in high amplitude δ Sct stars

It has been pointed out by earlier authors that radial pulsation seems to be the only type present in high amplitude δ Sct stars, at least for monoperiodic stars. In order to confirm this or not, we have collected all the multicolor data available for these stars in the Strömgren and Johnson photometric systems. Then, the type of pulsation has been analysed on the basis of the phase shifts and amplitude ratios between observed light and colour variations. The results indicate that all the stars analysed, including both high amplitude δ Sct (Population I) and SX Phe (Population II) stars, are radial pulsators. This is also true for the monoperiodic medium amplitude δ Sct stars analysed.This research was supported by the Junta de Andalucía and Dirección General de Investigación Científica y Técnica (DGICYT) under project PB93-0134