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

TL;DR

This study reanalyzed multisite observations of the roAp star HR 1217, revealing unexpected short-term variations in mode amplitudes and rotational modulation, suggesting complex magnetic and pulsational interactions.

Contribution

It provides a detailed reanalysis of historical data, introducing a weighting scheme and wavelet analysis to uncover rapid amplitude variability in HR 1217's pulsation modes.

Findings

Amplitude modulation varies with rotation as expected for certain modes

Unexpected short-term changes in pulsation amplitude and modulation profiles

Variations occur on timescales of days, indicating dynamic stellar processes

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.