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

Abstract

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.

Kepler main-sequence solar-like stars: surface rotation and magnetic-activity evolution

“…We opt to show both P rot and P seismic to demonstrate that both sets of measurements occupy the same parameter space. However, we note that there are some discrepancies between the seismic surface rotation periods (top right panel of Figure 10; Hall et al, 2021, see also Benomar et al, 2015;Breton et al, 2023). Some differences are expected, arising from differential rotation, as the observed acoustic modes are most sensitive to the subsurface layers (e.g., Basu et al, 2012;Benomar et al, 2015) and might be sensitive to different latitudes in comparison to the active-region latitudes.…”