A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry

摘要

Observations of Epsilon UMa obtained with the star tracker on the Wide FieldInfrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed.This is one of the most precise photometry of an Ap star. The amplitudespectrum is used to set an upper limit of 75 parts per million for theamplitude of stellar pulsations in this star unless it accidentally oscillateswith a single mode at the satellite orbit, its harmonics or their one dayaliases. This is the tightest limit put on the amplitude of oscillations in anAp star. As the rotation period of Epsilon UMa is relatively short (5.1 d), itcannot 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.