Asteroseismology of evolved stars to constrain the internal transport of angular momentum

Hartogh, J. W. den; Eggenberger, P.; Deheuvels, S.

doi:10.1051/0004-6361/202037568

Cited by 30 publications

(16 citation statements)

References 38 publications

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“…Eggenberger et al (2019b) showed that values of α significantly below unity (α ∼ 0.5) are needed to reproduce the internal rotation of the evolved subgiants studied by Deheuvels et al (2014), while matching the core rotation of stars on the RGB requires α ∼ 1.5. Moreover, even higher values of α are needed to account for the internal rotation of intermediate mass stars in the core He burning phase (den Hartogh et al 2020). To estimate the agreement of this formalism with the results of this study, we computed a model of KIC5955122 including the prescription of Fuller et al (2019) using the GENEC code.…”

Section: Comparison With Predictions From Potential Am Transport Mechmentioning

confidence: 98%

“…So far, their impact on the rotation evolution of subgiants and red giants has been addressed only under the debated assumption of the Tayler-Spruit dynamo in radiative interi-ors (Spruit 2002), and its revision based on a different saturation process by Fuller et al (2019). Comparisons with asteroseismic measurements have shown that this process is currently unable to correctly account for the internal rotation of subgiants and red giants (Cantiello et al 2014, den Hartogh et al 2019, Eggenberger et al 2019b, den Hartogh et al 2020.…”

Section: Introductionmentioning

confidence: 99%

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Seismic evidence for near solid-body rotation in two Kepler subgiants and implications for angular momentum transport

Deheuvels

Ballot

Eggenberger

et al. 2020

A&A

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Context. Asteroseismic measurements of the internal rotation of subgiants and red giants all show the need for invoking a more efficient transport of angular momentum than theoretically predicted. Constraints on the core rotation rate are available starting from the base of the red giant branch (RGB) and we are still lacking information on the internal rotation of less evolved subgiants. Aims. We identify two young Kepler subgiants, KIC8524425 and KIC5955122, whose mixed modes are clearly split by rotation. We aim to probe their internal rotation profile and assess the efficiency of the angular momentum transport during this phase of the evolution. Methods. Using the full Kepler data set, we extracted the mode frequencies and rotational splittings for the two stars using a Bayesian approach. We then performed a detailed seismic modeling of both targets and used the rotational kernels to invert their internal rotation profiles using the MOLA inversion method. We thus obtained estimates of the average rotation rates in the g-mode cavity (Ω g) and in the p-mode cavity (Ω p). Results. We found that both stars are rotating nearly as solid bodies, with core-envelope contrasts of Ω g/ Ω p = 0.68 ± 0.47 for KIC8524425 and Ω g/ Ω p = 0.72 ± 0.37 for KIC5955122. This result shows that the internal transport of angular momentum has to occur faster than the timescale at which differential rotation is forced in these stars (between 300 Myr and 600 Myr). By modeling the additional transport of angular momentum as a diffusive process with a constant viscosity ν add , we found that values of ν add > 5 × 10 4 cm 2 .s −1 are required to account for the internal rotation of KIC8524425, and ν add > 1.5 × 10 5 cm 2 .s −1 for KIC5955122. These values are lower than or comparable to the efficiency of the core-envelope coupling during the main sequence, as given by the surface rotation of stars in open clusters. On the other hand, they are higher than the viscosity needed to reproduce the rotation of subgiants near the base of the RGB. Conclusions. Our results yield further evidence that the efficiency of the internal redistribution of angular momentum decreases during the subgiant phase. We thus bring new constraints that will need to be accounted for by mechanisms that are proposed as candidates for angular momentum transport in subgiants and red giants.

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Section: Comparison With Predictions From Potential Am Transport Mechmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Seismic evidence for near solid-body rotation in two Kepler subgiants and implications for angular momentum transport

Deheuvels

Ballot

Eggenberger

et al. 2020

A&A

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“…In the recent literature that tackles this important question, most of the attention has been given to the potential effects of Maxwell stresses triggered by unstable fields in stably stratified radiative regions (e.g. Fuller et al 2019;Eggenberger et al 2020;Den Hartogh et al 2020;Jouve et al 2020). Here we recall the potentially significant efficiency with which a stable axisymmetric field redistributes angular momentum along poloidal field lines, a well-known result since Ferraro (1937), Mestel & Weiss (1987).…”

Section: Angular Momentum Transport By Fossil Magnetic Fields In Evolved Solar-like Starsmentioning

confidence: 99%

Magnetic signatures on mixed-mode frequencies

Bugnet

Prat

Mathis

et al. 2021

A&A

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Context. The discovery of moderate differential rotation between the core and the envelope of evolved solar-like stars could be the signature of a strong magnetic field trapped inside the radiative interior. The population of intermediate-mass red giants presenting surprisingly low-amplitude mixed modes (i.e. oscillation modes that behave as acoustic modes in their external envelope and as gravity modes in their core) could also arise from the effect of an internal magnetic field. Indeed, stars more massive than about 1.1 solar masses are known to develop a convective core during their main sequence. The field generated by the dynamo triggered by this convection could be the progenitor of a strong fossil magnetic field trapped inside the core of the star for the remainder of its evolution. Aims. Observations of mixed modes can constitute an excellent probe of the deepest layers of evolved solar-like stars, and magnetic fields in those regions can impact their propagation. The magnetic perturbation on mixed modes may therefore be visible in asteroseismic data. To unravel which constraints can be obtained from observations, we theoretically investigate the effects of a plausible mixed axisymmetric magnetic field with various amplitudes on the mixed-mode frequencies of evolved solar-like stars. Methods. First-order frequency perturbations due to an axisymmetric magnetic field were computed for dipolar and quadrupolar mixed modes. These computations were carried out for a range of stellar ages, masses, and metallicities. Conclusions. We show that typical fossil-field strengths of 0.1 − 1 MG, consistent with the presence of a dynamo in the convective core during the main sequence, provoke significant asymmetries on mixed-mode frequency multiplets during the red giant branch. We provide constraints and methods for the detectability of such magnetic signatures. We show that these signatures may be detectable in asteroseismic data for field amplitudes small enough for the amplitude of the modes not to be affected by the conversion of gravity into Alfvén waves inside the magnetised interior. Finally, we infer an upper limit for the strength of the field and the associated lower limit for the timescale of its action in order to redistribute angular momentum in stellar interiors.

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“…The physical mechanism is not yet understood, but some characterization of its behavior with evolutionary status or mass have been performed (Cantiello et al, 2014;Spada et al, 2016;Eggenberger et al, 2017Eggenberger et al, , 2019a. The proposed solution of a modified Tayler-Spruit magnetic dynamo (Fuller et al, 2019) has been shown to be unable to reproduce the observations of both red giants and sub-giants (Eggenberger et al, 2019b;den Hartogh et al, 2020). Explorations of the role of IGW (see section 5.1) in the angular momentum transport in red giants and sub-giants have shown that they are not efficient enough to solve the problem, though they could play a role (Fuller et al, 2014;Pinçon et al, 2017).…”

Section: Rotationmentioning

confidence: 99%

Massive Star Modeling and Nucleosynthesis

Ekström

2021

Front. Astron. Space Sci.

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After a brief introduction to stellar modeling, the main lines of massive star evolution are reviewed, with a focus on the nuclear reactions from which the star gets the needed energy to counterbalance its gravity. The different burning phases are described, as well as the structural impact they have on the star. Some general effects on stellar evolution of uncertainties in the reaction rates are presented, with more precise examples taken from the uncertainties of the 12C(α, γ)16O reaction and the sensitivity of the s-process on many rates. The changes in the evolution of massive stars brought by low or zero metallicity are reviewed. The impact of convection, rotation, mass loss, and binarity on massive star evolution is reviewed, with a focus on the effect they have on the global nucleosynthetic products of the stars.

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Asteroseismology of evolved stars to constrain the internal transport of angular momentum

Cited by 30 publications

References 38 publications

Seismic evidence for near solid-body rotation in two Kepler subgiants and implications for angular momentum transport

Seismic evidence for near solid-body rotation in two Kepler subgiants and implications for angular momentum transport

Magnetic signatures on mixed-mode frequencies

Massive Star Modeling and Nucleosynthesis

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