Angular momentum redistribution by mixed modes in evolved low-mass stars

Belkacem, K.; Marques, J. P.; Goupil, M. J.; Mosser, B.; Sonoi, T.; Ouazzani, R. M.; Dupret, Marc‐Antoine; Mathis, S.; Grosjean, M.

doi:10.1051/0004-6361/201526043

Cited by 75 publications

(50 citation statements)

References 48 publications

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“…The internal rotation rates of red giants, as measured by asteroseismology, is a few orders of magnitude smaller than what is predicted by rotating stellar models (Mosser et al 2012), indicating that one or several missing angular momentum transport processes are at work in these evolved stars (e.g. Fuller et al 2014;Rüdiger et al 2015;Belkacem et al 2015;Eggenberger et al 2017).…”

Section: Introductionmentioning

confidence: 83%

Deciphering the oscillation spectrum of γ Doradus and SPB stars

Christophe

Ballot

Ouazzani

et al. 2018

A&A

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Context. The space-based Kepler mission provided four years of highly precise and almost uninterrupted photometry for hundreds of γ Doradus stars and tens of SPB stars, finally allowing us to apply asteroseismology to these gravity mode pulsators. Without rotation, gravity modes are equally spaced in period. This simple structure does not hold in rotating stars for which rotation needs to be taken into account to accurately interpret the oscillation spectrum. Aims. We aim to develop a stellar-model-independent method to analyse and interpret the oscillation spectrum of γ Dor and SPB stars. Methods. Within the traditional approximation of rotation, we highlight the possibility of recovering the equidistance of period spacings by stretching the pulsation periods. The stretching function depends on the degree and azimuthal order of gravity modes and the rotation rate of the star. In this new stretched space, the pulsation modes are regularly spaced by the stellar buoyancy radius. Results. On the basis of this property, we implemented a method to search for these new regularities and simultaneously infer the rotation frequency and buoyancy radius. Tests on synthetic spectra computed with a non-perturbative approach show that we can retrieve these two parameters with reasonable accuracy along with the mode identification. In uniformly rotating models of a typical γ Dor star, and for the most observed prograde dipole modes, we show that the accuracy on the derived parameters is better than 5% on both the internal rotation rate and the buoyancy radius. Finally, we apply the method to two stars of the Kepler field, a γ Dor and an SPB, and compare our results with those of other existing methods. Conclusions. We provide a stellar-model-independent method to obtain the near-core rotation rate, the buoyancy radius and mode identification from g-mode spectra of γ Dor and SPB stars.

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Section: Introductionmentioning

confidence: 83%

Deciphering the oscillation spectrum of γ Doradus and SPB stars

Christophe

Ballot

Ouazzani

et al. 2018

A&A

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“…Other studies show that additional mixing is needed to explain observed rotation profiles of red giants or subgiants Ceillier et al 2012;Marques et al 2013). Moreover, even adding other transport processes is still not sufficient to explain the observations , for the Tayler-Spruit dynamo; Fuller et al 2014;Belkacem et al 2015, for internal gravity waves). Constraints from the spin of neutron stars and white dwarfs at birth also indicate that the transport as predicted by Zahn's model is not sufficient (Heger et al 2005, for neutron stars; Suijs et al 2008, for white dwarfs).…”

Section: Introductionmentioning

confidence: 93%

Shear mixing in stellar radiative zones

Prat

Guilet

Viallet

et al. 2016

A&A

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Context. Recent numerical simulations suggest that the model by Zahn (1992, A&A, 265, 115) for the turbulent mixing of chemical elements due to differential rotation in stellar radiative zones is valid. Aims. We investigate the robustness of this result with respect to the numerical configuration and Reynolds number of the flow. Methods. We compare results from simulations performed with two different numerical codes, including one that uses the shearingbox formalism. We also extensively study the dependence of the turbulent diffusion coefficient on the turbulent Reynolds number. Results. The two numerical codes used in this study give consistent results. The turbulent diffusion coefficient is independent of the size of the numerical domain if at least three large turbulent structures fit in the box. Generally, the turbulent diffusion coefficient depends on the turbulent Reynolds number. However, our simulations suggest that an asymptotic regime is obtained when the turbulent Reynolds number is larger than 10 3 . Conclusions. Shear mixing in the regime of small Péclet numbers can be investigated numerically both with shearing-box simulations and simulations using explicit forcing. Our results suggest that Zahn's model is valid at large turbulent Reynolds numbers.

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“…for a benchmark model. In a companion paper (Belkacem et al 2015, hereafter Paper II) we consider realistic mode amplitudes to quantitatively estimate the efficiency of the angular momentum transport by modes along the evolution of low-mass stars. This paper is organised as follows: Sect.…”

Section: Introductionmentioning

confidence: 99%

Angular momentum redistribution by mixed modes in evolved low-mass stars

Belkacem

Marques

Goupil

et al. 2015

A&A

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Seismic observations by the space-borne mission Kepler have shown that the core of red giant stars slows down while evolving, requiring an efficient physical mechanism to extract angular momentum from the inner layers. Current stellar evolution codes fail to reproduce the observed rotation rates by several orders of magnitude and instead predict a drastic spin-up of red giant cores. New efficient mechanisms of angular momentum transport are thus required. In this framework, our aim is to investigate the possibility that mixed modes extract angular momentum from the inner radiative regions of evolved low-mass stars. To this end, we consider the transformed Eulerian mean (TEM) formalism, which allows us to consider the combined effect of both the wave momentum flux in the mean angular momentum equation and the wave heat flux in the mean entropy equation as well as their interplay with the meridional circulation. In radiative layers of evolved low-mass stars, the quasi-adiabatic approximation, the limit of slow rotation, and the asymptotic regime can be applied for mixed modes and enable us to establish a prescription for the wave fluxes in the mean equations. The formalism is finally applied to a 1.3 M benchmark model, representative of observed CoRoT and Kepler oscillating evolved stars. We show that the influence of the wave heat flux on the mean angular momentum is not negligible and that the overall effect of mixed modes is to extract angular momentum from the innermost region of the star. A quantitative and accurate estimate requires realistic values of mode amplitudes. This is provided in a companion paper.

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Angular momentum redistribution by mixed modes in evolved low-mass stars

Cited by 75 publications

References 48 publications

Deciphering the oscillation spectrum of γ Doradus and SPB stars

Deciphering the oscillation spectrum of γ Doradus and SPB stars

Shear mixing in stellar radiative zones

Angular momentum redistribution by mixed modes in evolved low-mass stars

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