Variability in mode amplitudes in the rapidly oscillating Ap star HR 1217

Abstract

HR 1217 is one of the best-studied rapidly oscillating Ap (roAp) stars, with eight known oscillation modes that are distorted by a strong, global magnetic field. We have reanalysed the multisite observations of HR 1217 taken in 1986 and 2000. We determined a weighting scheme for the 1986 and 2000 data to minimize the noise level. A wavelet analysis of the data has found that the modulation of the amplitude due to rotation for all frequencies is, in general, consistent with the expected modulation for modified l=1, 2 or 3 modes. Unexpected variations in the rotational modulation are also seen, with variations in the modulation profile, time of maximal pulsation, and pulsational energy in each mode. Interestingly, these changes take place on a short timescale, of the order of days. We consider potential explanations for these behaviours.

9 pages, 9 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

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• K2 observations of the rapidly oscillating Ap star 33 Lib (HD 137949): new frequencies and unique non-linear interactions
• The search for roAp stars: null results and new candidates from Stroemgren-Crawford photometry