The discovery of 8.0-min radial velocity variations in the strongly magnetic cool Ap star HD 154708, a new roAp star

HD154708 has an extraordinarily strong magnetic field of 24.5 kG. Using 2.5 h of high time resolution Ultraviolet and Visual Echelle Spectrograph (UVES) spectra we have discovered this star to be an roAp star with a pulsation period of 8 min. The radial velocity amplitudes in the rare earth element lines of Nd II, Nd III and Pr III are unusually low - similar to 60 m s(-1) - for an roAp star. Some evidence suggests that roAp stars with stronger magnetic fields have lower pulsation amplitudes. Given the central role that the magnetic field plays in the oblique pulsator model of the roAp stars, an extensive study of the relation of magnetic field strength to pulsation amplitude is desirable.