Stars of late A/early F spectral types on the main sequence occupy a key region on the H-R diagram, wherein their atmospheres transition from being principally radiative at temperatures around 8000 K to being principally convective around 6000 K. On the warm side of this transition sit the coolest Ap stars, strongly magnetic stars exhibiting intense and non-uniform chemical peculiarities in their atmospheres. Many of these very cool Ap stars are rapidly oscillating (ro) Ap stars. These roAp stars are high-overtone, non-radial p-mode pulsators, exhibiting mode amplitudes that are modulated according to the local magnetic field strength.

In this talk I will review the properties of the coolest Ap stars and describe an ongoing experiment aimed at understanding the transition from the fossil magnetic fields of roAp stars to the dynamo fields of solar-type stars as a consequence of convective field processing by the growing hydrogen convection zone.