Abstract
Observations of ǫ UMa obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed. This is one of the most precise photometry of an Ap star. The amplitude spectrum is used to set an upper limit of 75 parts per million for the amplitude of stellar pulsations in this star unless it accidentally oscillates with a single mode at the satellite orbit, its harmonics or their one day aliases. This is the tightest limit put on the amplitude of oscillations in an Ap star. As the rotation period of
ǫ UMa is relatively short (5.1 d), it cannot be argued that the observations were made at a wrong rotational phase. Our results thus
support the idea that some Ap stars do not pulsate at all.