Title: Second Overtone Pulsators among δ Scuti Stars
Abstract: We investigate the modal stability of stellar models at masses and luminosity levels corresponding to post-main-sequence luminous δ Scuti pulsators. The envelope models have been computed at fixed mass value (M/M☉ = 2.0), luminosity level [log (L/L☉) = 1.7], and chemical composition (Y = 0.28, Z = 0.02). According to a nonlinear approach to radial oscillations, the present investigation for the first time predicts the occurrence of stable second overtone pulsators . More generally, we found that when moving inside the instability strip from lower to higher effective temperatures, the models show a stable limit cycle in three different pulsation modes: fundamental and first and second overtones. The shapes of both light and velocity curves are presented and discussed, providing a useful tool for the identification of second overtone pulsators among the known groups of radially pulsating stars.