Microvariability in high-amplitude delta Scuti radially pulsating stars

Analyses of existing data of high-amplitude delta Scuti stars (HADS) show that variability, at the mmag level, is a common phenomenon among them. Detailed period analyses show that, apart from the already known case of AI Vel, two other stars -SX Phe and DY Peg - are also pulsating with more radial and/or non-radial periods than usually believed. The phenomenon, only visible when high-quality observations are available, can be of considerable interest because of the tight constraints that this imposes on the theoretical models.