Comparative seismology of pre- and main sequence stars in the instability strip

Pulsational properties of 1.8 M-circle dot stellar models covering the late st stages of contraction toward the main sequence up to early hydrogen burn ing phases are investigated by means of linear nonadiabatic analyses. Resul ts confirm that pre-main sequence stars (pms) which cross the classical ins tability strip on their way toward the main sequence are pulsationally unst able with respect to the classical opacity mechanisms. For both pms and mai n sequence types of models in the lower part of the instability strip, the unstable frequency range is found to be roughly the same. Some non-radial u nstable modes are very sensitive to the deep internal structure of the star . It is shown that discrimination between pms and main sequence stages is p ossible using differences in their oscillation frequency distributions in t he low frequency range.