Abstract
In this work we consider the sensitivity of gravity-mode period spacings to sharp changes in the inner structure of red giant stars, more specifically in the buoyancy frequency inside the g-mode propagation cavity. Based on a comparison between the solutions to the linear pulsation equations in the Cowling approximation for pure g-modes with results obtained with a full oscillation code we identify and correctly interpret the signature of the above-mentioned sharp variations in the period spacings. Two examples, of red giant models in different evolutionary phases, are discussed. Detection of these signatures in CoRoT, Kepler or future PLATO red-giant stars would pin down their evolutionary state in an unprecedented way.
Highlights
Red giant stars exhibit oscillations of mixed character, characterized by having the properties of an internal gravity wave (g-mode) in the deeper layers of the star, while maintaining the properties of an acoustic wave (p-mode) in the stellar envelope
Sharp variations in the buoyancy frequency can shift the periods of g-modes away from their asymptotic values and, leave a signature in the period spacings
We will provide two examples of the effect that sharp variations in the buoyancy frequency may leave on the period spacings of red giant stars
Summary
Red giant stars exhibit oscillations of mixed character, characterized by having the properties of an internal gravity wave (g-mode) in the deeper layers of the star, while maintaining the properties of an acoustic wave (p-mode) in the stellar envelope. Gravity waves propagate only where there is no convection and both their propagation cavity and periods depend on the buoyancy frequency. Sharp variations in the buoyancy frequency can shift the periods of g-modes away from their asymptotic values and, leave a signature in the period spacings (defined as the difference between the periods of modes of the same degree and consecutive radial orders). We will provide two examples of the effect that sharp variations in the buoyancy frequency may leave on the period spacings of red giant stars.
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