Red giants rotational splittings

R.M Ouazzani,M.J Goupil,J.P Marques,M.A Dupret

doi:10.1051/epjconf/20134303011

Abstract

The space missions CoRoT and Kepler provide high quality data that allow 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 giant 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 (1) that accounts for the effect of rotation on pulsations, and solves the pulsations eigenproblem directly for dipolar oscillation modes. We find that the limit of the perturbation to first order can be expressed in terms of the core rotation and the period separation between consecutive dipolar modes. Above this limit, each family of modes with different azimuthal symmetry m ,h as to be considered separately. For rapidly rotating red giants, new seismic diagnostics can be found for rotation by exploiting the differences between the period spacings associated with each m-family of modes.

Highlights

The CoRoT [2] and Kepler [3] spacecrafts have dramatically improved the quality of the available asteroseismic data
For rapidly rotating red giants, new seismic diagnostics can be found for rotation by exploiting the differences between the period spacings associated with each m-family of modes
Among the observed spectra of red giant stars, some show structures with nearly symmetric spacings around axisymmetric modes. For this kind of spectra, we found that one can figure out if these apparent multiplets split by rotation correspond to the original splittings by plotting the apparent splittings as a function of the axi-symmetric modes frequencies

Summary

INTRODUCTION

The CoRoT [2] and Kepler [3] spacecrafts have dramatically improved the quality of the available asteroseismic data. The values of the corresponding splittings are quite small and the use of the lowest order approximation to derive the splittings from stellar models for comparison can be justified Such studies led to the determination of unexpectedly low central rotation frequencies (of a few hundreds of nHz). A large set of red giant stars show complex frequency spectra, in particular with non symmetric multiplets and these stars are likely fast rotators Their rotation must be investigated with nonperturbative methods. We adopt the non-perturbative approach in order to shed light on the behaviour of splitted mixed modes in red giants spectra

THEORETICAL FREQUENCY SPECTRA FOR ROTATING RED GIANTS

SLOW TO MODERATE CORE ROTATING RED GIANTS

RAPID CORE ROTATING RED GIANTS

DISCUSSIONS AND CONCLUSIONS