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

Context. Asteroseismology experienced a breakthrough in the last two decades thanks to the so-called photometry revolution with space-based missions such as CoRoT, Kepler, and TESS. Because asteroseismic modelling will be part of the pipeline of the future PLATO mission, it is relevant to compare some of the current modelling strategies and discuss the limitations and remaining challenges for PLATO. In this first paper, we focused on modelling techniques treating directly the seismic information. Aims. We compared two modelling strategies by directly fitting the individual frequencies or by coupling a mean density inversion with a fit of the frequency separation ratios. Methods. We applied these two modelling approaches to six synthetic targets with a patched atmosphere, for which the observed frequencies were obtained with a non-adiabatic oscillation code. We then studied ten actual targets from the Kepler LEGACY sample. Results. As is well known, the fit of the individual frequencies is very sensitive to the surface effects and to the choice of the underlying prescription for semi-empirical surface effects. This significantly limits the accuracy and precision that can be achieved for the stellar parameters. The mass and radius tend to be overestimated, and the age therefore tends to be underestimated. In contrast, the second strategy, which is based on mean density inversions and on the ratios, efficiently damps the surface effects and allows us to obtain precise and accurate stellar parameters. The average statistical precision of our selection of targets from the LEGACY sample with this second strategy is 1.9% for the mass, 0.7% for the radius, and 4.1% for the age. This is well within the PLATO mission requirements. The addition of the inverted mean density to the constraints significantly improves the precision of the stellar parameters by 20%, 33%, and 16% on average for the stellar mass, radius, and age, respectively. Conclusions. The modelling strategy based on mean density inversions and frequencies separation ratios showed promising results for PLATO because it achieved a precision and accuracy on the stellar parameters that meet the PLATO mission requirements with ten Kepler LEGACY targets. The strategy also left some margin for other unaccounted systematics, such as the choice of the physical ingredients of the stellar models or the stellar activity.

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In search of gravity mode signatures in main sequence solar-type stars observed by Kepler

Breton,

Dhouib,

García

et al. 2023

A&A

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Gravity modes (g modes), mixed gravito-acoustic modes (mixed modes), and gravito-inertial modes (gi modes) possess unmatched properties as probes for stars with radiative interiors. The structural and dynamical constraints that they are able to provide cannot be accessed by other means. While they provide precious insights into the internal dynamics of evolved stars as well as massive and intermediate-mass stars, their non-detection in main sequence (MS) solar-type stars make them a crucial missing piece in our understanding of angular momentum transport in radiative zones and stellar rotational evolution. In this work, we aim to apply certain analysis tools originally developed for helioseismology in order to look for g-mode signatures in MS solar-type stars. We select a sample of the 34 most promising MS solar-type stars with Kepler four-year long photometric time series. All these stars are well-characterised late F-type stars with thin convective envelopes, fast convective flows, and stochastically excited acoustic modes (p modes). For each star, we compute the background noise level of the Fourier power spectrum to identify significant peaks at low frequency. After successfully detecting individual peaks in 12 targets, we further analyse four of them and observe distinct patterns of surrounding peaks with a low probability of being noise artifacts. Comparisons with the predictions from reference models suggest that these patterns are compatible with the presence of non-asymptotic low-order pure g modes, pure p modes, and mixed modes. Given their sensitivity to both the convective core interface stratification and the coupling between p- and g-mode resonant cavities, such modes are able to provide strong constraints on the structure and evolutionary states of the related targets. Considering the granulation and activity background of the stars in our sample, we subsequently compute the corresponding mode velocity necessary to trigger a detectable luminosity fluctuation. We use it to estimate the surface velocity, ⟨vr⟩, of the candidate modes we have detected. In this case, we find ⟨vr⟩∼10 cm s−1. These results could be extremely useful for characterising the deep interior of MS solar-type stars, as the upcoming PLATO mission will considerably expand the size of the available working sample.

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

Cited by 10 publications

References 69 publications

Mixing processes in stars

Mixing processes in stars

Asteroseismic modelling strategies in the PLATO era

In search of gravity mode signatures in main sequence solar-type stars observed by Kepler

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