Abstract
Stellar oscillations give seismic information on the internal properties of stars. Red giants are targets of interest since they present mixed modes, which behave as pressure modes in the convective envelope and as gravity modes in the radiative core. Mixed modes thus directly probe red giant cores, and allow in particular the study of their mean core rotation. The high-quality data obtained by CoRoT and Kepler satellites represent an unprecedented perspective to obtain thousands of measurements of red giant core rotation, in order to improve our understanding of stellar physics in deep stellar interiors. We developed an automated method to obtain such core rotation measurements and validated it for stars on the red giant branch. In this work, we particularly focus on the specific application of this method to red giants having a rapid core rotation. They show complex spectra where it is tricky to disentangle rotational splittings from mixed-mode period spacings. We demonstrate that the method based on the identification of mode crossings is precise and efficient. The determination of the mean core rotation directly derives from the precise measurement of the asymptotic period spacing {\Delta}{\Pi}1 and of the frequency at which the crossing of the rotational components is observed.
Highlights
Red giant stars are known to exhibit solar-like oscillations, corresponding mostly to pressure modes resulting from acoustic waves stochastically excited by turbulent convection in the external envelope
The space based CoRoT and Kepler missions have revealed that red giants present mixed modes, which behave as pressure modes in the convective envelope and as gravity modes in the radiative interior [3]
In the Astro Fluid 2016 Conference Proceedings edited by EAS Publications Series, we present in detail the method we developed in order to obtain automated measurements of the mean core rotation of red giants, and validate it for stars on the red giant branch (RGB), for which automated measurements are fully consistent with manual measurements [5]
Summary
Red giant stars are known to exhibit solar-like oscillations, corresponding mostly to pressure modes resulting from acoustic waves stochastically excited by turbulent convection in the external envelope. Dipole mixed modes allow us to identify the evolutionary stage of evolved stars: it is possible to distinguish core-helium burning stars from hydrogen-shell burning stars [4]. They provide the measurement of the asymptotic period spacing ∆Π1 [5] which is linked to the size of the core [6]. In this work we focus in particular on red giants with a rapid core rotation, where the rotational splittings are larger than half the mixed-mode spacing and complicate the interpretation of the spectra
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