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

Moyano, F.; Eggenberger, P.; Meynet, Georges; Gehan, Charlotte; Mosser, B.; Buldgen, G.; Salmon, Sébastien

doi:10.1051/0004-6361/202243389

Cited by 12 publications

(12 citation statements)

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“…According to the extant models, mixing induced by rotation produces a marginal effect on the TDU, while it could modify the 13 C-pocket, after its formation, and the consequent s-process nucleosynthesis. Nevertheless, recent asteroseismic studies of evolved low-mass stars revealed that most of the internal angular momentum is lost before the AGB phase, so that rotation likely does not play a relevant role in the AGB evolution and nucleosynthesis (see, e.g., [21] and references therein). More promising is the hypothesis of mixing induced by internal gravity wave (IGW) generated at the boundary of the convective envelope [22].…”

Section: Boundary Mixing and Extra-mixingmentioning

confidence: 99%

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The carbon star mystery: 40 years later

2023

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In 1981 Icko Iben Jr published a paper entitled “The carbon star mystery: why do the low mass ones become such, and where have all the high mass ones gone?”, where he discussed the discrepancy between the theoretical expectation and its observational counterpart about the luminosity function of AGB carbon stars. After more than 40 years, our understanding of this longstanding problem is greatly improved, also thanks to more refined stellar models and a growing amount of observational constraints. In this paper we review the state of the art of these studies and we briefly illustrate the future perspectives.

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Section: Boundary Mixing and Extra-mixingmentioning

confidence: 99%

“…[7], and references therein). As a matter of fact, the s-process enhancement observed in normal C stars is mainly due to the 13 C neutron burst, while the 22 Ne source only provides a marginal contribution. The presence of Tc alive ( 99 Tc half-life 2.11 × 10 5 yr) in the atmosphere of C stars is a probe of their intrinsic nature.…”

Section: Introductionmentioning

confidence: 99%

The carbon star mystery: 40 years later

2023

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“…Key observational constraints have been obtained for subgiant and red giant stars with the asteroseismic determination of the core rotation rates for a large sample of these evolved stars (Beck et al 2012;Deheuvels et al 2012Deheuvels et al , 2014Deheuvels et al , 2015Deheuvels et al , 2017Di Mauro et al 2016Mosser et al 2012;Gehan et al 2018;Fellay et al 2021). Comparisons with rotating models have then revealed the need for an efficient AM transport mechanism in addition to meridional circulation and transport by the shear instability (Eggenberger et al 2012;Ceillier et al 2013;Marques et al 2013;Eggenberger et al 2017Eggenberger et al , 2019Moyano et al 2022). Detailed asteroseismic studies of the internal rotation for some main-sequence (MS) stars, in particular, for γ Dor pulsators, also suggested that an efficient transport of AM operates in the radiative zones of these stars, similarly to the conclusion obtained for the Sun and evolved stars (e.g.…”

Section: Introductionmentioning

confidence: 99%

Testing angular momentum transport processes with asteroseismology of solar-type main-sequence stars

Bétrisey¹,

Eggenberger²,

Buldgen³

et al. 2023

A&A

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Context. Thanks to the so-called photometry revolution with the space-based missions CoRoT, Kepler, and TESS, asteroseismology has become a powerful tool to study the internal rotation of stars. The rotation rate depends on the efficiency of the angular momentum (AM) transport inside the star, and its study allows to constrain the internal AM transport processes, as well as improve our understanding of their physical nature. Aims. We compared the ratio of the rotation rate predicted by asteroseismology and starspot measurements of solar-type stars considering different AM transport prescriptions and investigated whether some of these prescriptions can be ruled out observationally. Methods. We conducted a two-step modelling procedure of four main-sequence stars from the Kepler LEGACY sample, which consists of an asteroseismic characterisation that serves as a guide for a modelling with rotating models, including a detailed and coherent treatment of the AM transport. The rotation profiles derived with this procedure were used to estimate the ratio of the mean asteroseismic rotation rate with the surface rotation rate from starspot measurements for each AM transport prescriptions. Comparisons between the models were then conducted. Results. In the hotter part of the Hertzsprung-Russell (HR) diagram (masses typically above ∼ 1.2M at solar metallicity), models with only hydrodynamic transport processes and models with additional transport by magnetic instabilities are found to be consistent with previous measurements that observed a low degree (below 30%) of radial differential rotation between the radiative and convective zones. For these stars, which constitute a significant fraction of the Kepler LEGACY sample, a combination of asteroseismic constraints from the splitting of pressure modes and of the surface rotation rate does not allow us to conclude that an efficient AM transport is required in addition to transport by meridional circulation and shear instability alone. Even a model assuming local AM conservation cannot be ruled out. In the colder part of the HR diagram, the situation is different because of the efficient braking of the stellar surface by magnetised winds. We find a clear disagreement between the rotational properties of models that only include hydrodynamic processes and asteroseismic constraints, while models with magnetic fields correctly reproduce the observations, similarly to the solar case. Conclusions. This shows the existence of a mass regime corresponding to main-sequence F-type stars for which it is difficult to constrain the AM transport processes, unlike for hotter, Gamma Dor stars or colder, less massive solar analogues. The comparison between asteroseismic measurements and surface rotation rates enables us to easily rule out models with an inefficient transport of AM in the colder part of the HR diagram.

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“…In addition, the transport of angular momentum have been shown to be varying along evolution with an efficient transport during the MS, then a decreasing phase along SGB, and, finally, a new increase during the RGB phase (e.g. Deheuvels et al 2014Deheuvels et al , 2020Spada et al 2016;Eggenberger et al 2019a,b;Moyano et al 2022Moyano et al , 2023. These observational constraints suggest the action of an additional unknown transport of angular momentum whose identification remains an open question.…”

Section: Introductionmentioning

confidence: 99%

Angular momentum and lithium transport from main sequence to sub-giant and red giant low-mass stars

Dumont¹

2023

A&A

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Context. Asteroseismology provides a unique opportunity to probe the interiors of evolved stars and constrain their internal rotation. The correct reproduction of the core rotation evolution has not yet been achieved, although it is key to understanding the internal processes involved in low-mass stars. Aims. We explore the efficiency required to reproduce the general behaviour of the transport of angular momentum along the evolution in view of asteroseismic constraints from giant low-mass stars. We analyse the consequences and predictions for lithium and beryllium surface abundances from the main sequence to red giant phase. Methods. We computed a series of models, which included atomic diffusion, rotation-induced mixing, magnetic braking, and additional processes tailored for main sequence low-mass stars. We extended these models to more evolved phases and investigated an updated angular momentum transport by including a time-dependent extra viscosity related to the azimuthal magneto-rotational instability. We compared our predictions to the asteroseismic measurements of the core and surface rotation of a sample of sub-giant and red giant stars. We compared the model predictions for the lithium and beryllium surface evolution with the available observations. Results. We confirm that a time-dependent additional viscosity ν add (t) is required to reproduce the general behaviour of the core rotation rate along successive stellar evolutionary phases given the dependence on the differential rotation and the mass. We show that it results in stronger lithium and beryllium depletions for low-mass stars over evolution. We confirm that predicted lithium abundances at the red giant bump by classical models, commonly used as references, cannot reproduce the lithium depletion along the main sequence and evolved phases of stellar evolution. We show that the observed amount of lithium of stars less massive than 1M ⊙ leads to a discrepancy between model predictions and observations at the red giant bump. Conclusions. We show that a semi-parametric model can reproduce the rotational behaviour along the first phases of evolution well, with the exception of the sharp transition observed during the sub-giant phase. This suggests that two distinct transport processes may be involved. The processes required to transport chemicals during the main sequence phase and angular momentum until the red giant phase impact the lithium depletion all along the evolutionary duration. A good prediction of the lithium abundance at young phases places strong constraints on the predicted one at more evolved phases. It also highlights discrepancies between models and observations for the lowest mass stars and impacts the threshold that defines lithium-rich giant stars, showing that classical models tend to overestimate this threshold.

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

Cited by 12 publications

References 77 publications

The carbon star mystery: 40 years later

The carbon star mystery: 40 years later

Testing angular momentum transport processes with asteroseismology of solar-type main-sequence stars

Angular momentum and lithium transport from main sequence to sub-giant and red giant low-mass stars

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