Asteroseismology of the dip structure in period-spacings of rapidly rotating gamma Doradus stars caused by the coupling between core and envelope oscillations

Abstract

Recent asteroseismic observations by the $Kepler$ space mission have revealed the dip fine structure in the period-spacing versus period diagram of rapidly rotating $\gamma$ Doradus stars. Following the successful reproduction of the dip structure by numerical calculations in previous studies, we present in this paper the physical mechanism of how the dip is formed as a result of the interaction between the gravito-inertial waves in the radiative envelope and the pure inertial waves in the convective core. We analytically describe the wave solutions in both of the radiative envelope and the convective core, and match them at the interface to construct an eigenmode. We have found from the analysis the following points: the dip structure is mainly controlled by a parameter that has an inverse correlation with Brunt-Väisälä frequency at the interface; the depth and the width of the dip is shallower and larger, respectively, as the parameter gets large; the shape of the dip can be approximated by the Lorentzian function; the period at the central position of the dip is equal to or slightly smaller than that of the involved pure inertial mode in the convective core. We have also understood based on the evolutionary models of main-sequence stars that the parameter is inversely correlated with the chemical composition gradient at the convective-core boundary. The dip structure thus would provide information about the poorly-understood physical processes, such as diffusion, convective overshooting and rotational mixing, around the boundary between the convective core and the radiative envelope.

20 pages, 15 figures, Accepted to MNRAS

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Cited by in corpus (5)

• Tidally perturbed g-mode pulsations in a sample of close eclipsing binaries
• Angular momentum transport near convective-core boundaries of Gamma Doradus stars
• Mode coupling coefficients between the convective core and radiative envelope of $\gamma$Doradus and slowly pulsating B stars
• Properties of observable mixed inertial and gravito-inertial modes in γ Doradus stars
• Constraining differential rotation in gamma Doradus stars from inertial dips properties