Non-perturbative effect of rotation on dipolar mixed modes in red giant stars

Abstract

The space missions CoRoT and Kepler provide high quality data that allow us to test the transport of angular momentum in stars by the seismic determination of the internal rotation profile. Our aim is to test the validity of the seismic diagnostics for red giants rotation that are based on a perturbative method and to investigate the oscillation spectra when the validity does not hold. We use a non-perturbative approach implemented in the ACOR code (Ouazzani et al. 2012) that accounts for the effect of rotation on pulsations, and solves the pulsation eigenproblem directly for dipolar oscillation modes. We find that the limit of the perturbation to first order can be expressed in terms of the rotational splitting compared to the frequency separation between consecutive dipolar modes. Above this limit, non-perturbative computations are necessary but only one term in the spectral expansion of modes is sufficient as long as the core rotation rate remains significantly smaller than the pulsation frequencies. Each family of modes with different azimuthal symmetry, m, has to be considered separately. In particular, in case of rapid core rotation, the density of the spectrum differs significantly from one m-family of modes to another, so that the differences between the period spacings associated with each m-family can constitute a promising guideline toward a proper seismic diagnostic for rotation.

5 pages, 5 figures, accepted for publication in A&A

References in corpus (5)

• Spin down of the core rotation in red giants
• Seismic diagnostics for transport of angular momentum in stars 1. Rotational splittings from the PMS to the RGB
• Angular momentum transport in stellar interiors constrained by rotational splittings of mixed modes in red giants
• Seismic diagnostics for transport of angular momentum in stars 2. Interpreting observed rotational splittings of slowly-rotating red giant stars
• Pulsations of rapidly rotating stars: I. The ACOR numerical code

Cited by in corpus (17)

• Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants
• Angular momentum transport within evolved low-mass stars
• Giant star seismology
• Core rotation braking on the red giant branch for various mass ranges
• Period spacings in red giants I. Disentangling rotation and revealing core structure discontinuities
• Period spacings in red giants IV: Toward a complete description of the mixed-mode pattern
• Theoretical power spectra of mixed modes in low mass red giant stars
• Study of KIC 8561221 observed by Kepler: an early red giant showing depressed dipolar modes
• Magnetic signatures on mixed-mode frequencies. I. An axisymmetric fossil field inside the core of red giants
• Magnetic signatures on mixed-mode frequencies. II. Period spacings as a probe of the internal magnetism of red giants
• Mode Mixing and Rotational Splittings: II. Reconciling Different Approaches to Mode Coupling
• Automated determination of g-mode period spacing of red-giant stars
• Mode Mixing and Rotational Splittings: I. Near-Degeneracy Effects Revisited
• Sounding stellar cores with mixed modes
• Inequalities on stellar rotational splittings derived from assumptions on the rotation profile
• Internal rapid rotation and its implications for stellar structure and pulsations
• Stellar oscillations - the adiabatic case