Échelle diagrams and period spacings of g modes in γ Doradus stars from four years of Kepler observations

Abstract. We use photometry from the Kepler Mission to study oscillations in γ Do-radus stars. Some stars show remarkably clear sequences of g modes and we use period échelle diagrams to measure period spacings and identify rotationally split multiplets with = 1 and = 2. We find small deviations from regular period spacings that arise from the gradient in the chemical composition just outside the convective core. We also find stars for which the period spacing shows a strong linear trend as a function of period, consis-tent with relatively rapid rotation. Overall, the results indicate it will be possible to apply asteroseismology to a range of γ Dor stars. Gravity modes are extremely valuable for probing stellar interiors. Asteroseismology using g modes has so far produced very good results on three classes of highly evolved stars, namely white dwarfs [1], sdB stars [2] and red giants [3–5]. Excellent results have also been obtained for a few SPB stars (slowly pulsating B stars), which lie on the upper main sequence [6,7]. However, the g modes lower on the main sequence, which occur in γDoradus stars, have proved much more difficult to exploit. They typically have periods close to one day, which makes ground-based study exceedingly difficult. Fur-thermore, as we show here, they have very dense frequency spectra. Even the first month or so o