Amplitude Variability in gamma Dor and delta Scuti stars observed by the Kepler Spacecraft

TL;DR

This paper investigates amplitude variability in gamma Dor and delta Scuti stars using Kepler data, applying wavelet analysis to identify and characterize amplitude changes over time.

Contribution

It introduces a wavelet-based analysis approach to detect and analyze amplitude variations in pulsating stars observed by Kepler, focusing on faint stars and short timescales.

Findings

Amplitude variations are detectable in Kepler data for faint stars.

Amplitude variability occurs over specific timescales and magnitudes.

No consistent correlation between amplitude changes of different frequencies was found.

Abstract

The NASA Kepler spacecraft data revealed a large number of multimode nonradially pulsating gamma Dor and delta Sct variable star candidates. The high precision long time-series photometry makes it possible to study amplitude variations of the frequencies. We summarize recent literature on amplitude and frequency variations in pulsating variables. We are searching for amplitude variability in several dozen faint gamma Doradus or delta Scuti variable-star candidates observed as part of the Kepler Guest Observer program. We apply several methods, including a Matlab-script wavelet analysis developed by J. Jackiewicz, and the wavelet technique of the VSTAR software (http://www.aavso.org/vstar-overview). Here we show results for two stars, KIC 2167444 and KIC 2301163. We discuss the magnitude and timescale of the amplitude variations, and the presence or absence of correlations between amplitude variations for different frequencies of a given star. Amplitude variations may be detectable using Kepler data even for stars with Kepler magnitude >14 with low-amplitude frequencies (around 100 ppm) using only one or a few quarters of long-cadence data. We discuss proposed causes of amplitude spectrum variability that will require further investigation.