  We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR
1217) based on nonadiabatic analyses taking into account the effect of dipole
magnetic fields. We have found that all the pulsation modes appropriate for HD
24712 are damped; i.e., the kappa-mechanism excitation in the hydrogen
ionization layers is not strong enough to excite high-order p-modes with
periods consistent with observed ones, all of which are found to be above the
acoustic cut-off frequencies of our models.
  The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with
modified $l=2$ and $l=3$ modes, respectively. The large frequency separation
($\approx 68 \mu$Hz) is reproduced by models which lay within the error box of
HD 24712 on the HR diagram. The nearly equally spaced frequencies of HD 24712
indicate the small frequency separation to be as small as $\approx 0.5\mu$Hz.
However, the small separation derived from theoretical $l=1$ and 2 modes are
found to be larger than $\sim 3\mu$Hz. The problem of equal spacings could be
resolved by assuming that the spacings correspond to pairs of $l=2$ and $l=0$
modes. The amplitude distribution on the stellar surface is strongly affected
by the magnetic field resulting in the predominant concentration at the polar
regions.
  Amplitudes and phases of radial-velocity variations for various spectral
lines are converted to relations of amplitude/phase versus optical depth in the
atmosphere. Oscillation phase delays gradually outward in the outermost layers
indicating the presence of waves propagating outward. The phase changes steeply
around $\log\tau\sim-3.5$, which supports a $T-\tau$ relation having a small
temperature inversion there.
