Oscillation mode variability in evolved compact pulsators from Kepler photometry. II. Comparison of modulationpatterns between raw and corrected flux

Abstract

We present the second results of an ensemble and systematic survey of oscillation mode variability in compact pulsators observed with the original {\sl Kepler} mission. Two types of flux calibrations, raw and corrected, collected on two hot B subdwarf stars, KIC\,2438324 and KIC\,11179657, are thoroughly examined with the goal to evaluate the difference of patterns when oscillation modes modulate in amplitude (AM) and frequency (FM). We concentrate on AMs and FMs occurring in seven multiplet components in each star as representative frequencies. The analysis shows that FM measurements are independent of the flux calibration we choose. However, if flux contamination by nearby stars is large, AMs may be significantly different between raw and corrected flux. In addition, AMs suffer, to some extent, from systematic modulation pattern which is most likely induced by instrumental effects {and} differs from one star to another. Our results indicate that stars with no contamination are better candidates to quantitatively compare modulation patterns with theory and should be given a higher priority for such studies, since light contamination will destroy real amplitude modulation patterns.