Detecting non-uniform period spacings in theKeplerphotometry ofγDoradus stars: methodology and case studies

Abstract

Context. The analysis of stellar oscillations is one of the most reliable ways to probe stellar interiors. Recent space missions such as Kepler have provided us with an opportunity to study these oscillations with unprecedented detail. For many multi-periodic pulsators such as γ Doradus stars, this led to the detection of dozens to hundreds of oscillation frequencies that could not be found from groundbased observations. Aims. We aim to detect non-uniform period spacings in the Fourier spectra of a sample of γ Doradus stars observed by Kepler. Such detection is complicated by both the large number of significant frequencies in the space photometry and by overlapping nonequidistant rotationally split multiplets. Methods. Guided by theoretical properties of gravity-mode oscillation of γ Doradus stars, we developed a period-spacing detection method and applied it to Kepler observations of a few stars, after having tested the performance from simulations. Results. The application of the technique resulted in the clear detection of non-uniform period spacing series for three out of the five treated Kepler targets. Disadvantages of the technique are also discussed, and include the disability to distinguish between different values of the spherical degree and azimuthal order of the oscillation modes without additional theoretical modelling. Conclusions. Despite the shortcomings, the method is shown to allow solid detections of period spacings for γ Doradus stars, which will allow future asteroseismic analyses of these stars.

Convection and Overshoot in Models of γ Doradus and δ Scuti Stars

“…We confirm previous trends detected by Ouazzani et al (2016) and Van Reeth et al (2015. We also find that the m = −1 modes may provide a useful diagnostic of rotation rate, as the upward slope of the period spacings becomes steeper as the rotation rate increases.…”

“…The γ Doradus variables are expected to display regular patterns in the period spacing (Van Reeth et al 2015Ouazzani et al 2016). As found by these previous studies, we find that in non-rotating models, the period spacings are nearly flat as a function of period, as shown in Figure 7.…”

“…First, as noted by Van Reeth et al (2015), the increased mixing caused by convective overshooting tends to wash out the chemical discontinuity, so the dips in the period spacing pattern become smaller, as shown in Figure 7. We also find that increased convective overshoot increases the absolute value of the period spacing.…”

Near-uniform internal rotation of the main-sequence γ Doradus pulsator KIC 7661054

“…ν k = νi + νj, which are known to exist in g mode pulsators Van Reeth et al 2015b). This possibility cannot be definitively ruled out because a large number of potential parent modes allows virtually any peak to be explained as a linear combination, but the absence of strong combinations at frequencies with simple relationships to their parent modes (such as 2ν1 or ν1 + ν2) argues against this origin (Pápics 2012).…”

Constraining the near-core rotation of theγDoradus star 43 Cygni using BRITE-Constellation data

“…Spurious extracted frequencies may be caused by, e.g., the attempted prewhitening of unresolved pulsation frequencies and/or the residuals of imperfect preceding prewhitening. Hence, to facilitate the search for period spacing patterns in the data, we used the evaluation criterion defined by Van Reeth et al (2015a) to help assess the reliability of the extracted signal, and classified the pulsation periods in nine different groups accordingly. In this evaluation we compared the amplitudes of the extracted pulsations with the local value of the Lomb-Scargle periodogram at that pulsation period.…”