  Some of the rapidly oscillating (CP2) stars, have frequencies which are
larger than the theoretical acoustic cut-off frequency. As the cut-off
frequency depends on the T(tau) relation in the atmosphere, we have computed
models and adiabatic frequencies for pulsating Ap stars with T(tau) laws based
on Kurucz model atmospheres and on Hopf's purely radiative relation.
  The frequency-dependent treatment of radiative transfer as well as an
improved calculation of the radiative pressure in Kurucz model atmospheres
increase the theoretical acoustic cut-off frequency by about 200 microHz, which
is closer to the observations.
  For alpha Cir we find models with Kurucz atmospheres which have indeed a
cut-off frequency beyond the largest observed frequency and which are well
within the Teff - L error box. For HD 24712 only models which are hotter by
about 100 K and less luminous by nearly 10% than what is actually the most
probable value would have an acoustic cut-off frequency large enough.
  One may thus speculate that the old controversy about a mismatch between
observed largest frequencies and theoretical cut-off frequencies of roAp star
models is resolved. However, the observational errors for the astrophysical
fundamental parameters have to be reduced further and the model atmospheres
refined.
  Further details can be found in Audard et al. (1997)
