27 septembre 2022
Titre: Rotation and dynamics of main-sequence solar-type stars in the PLATO era
Par : Sylvain Breton (INAF – Osservatorio Astrofisico di Catania)
Setting constraints on the rotation profile, both radial and latitudinal, of main-sequence solar-type stars, from the surface to the core, is a fundamental problem if we want to improve our understanding of stellar evolution (especially in order to get better estimates of stellar ages) and of the interactions of stars with their environment, especially exoplanets. As of today, the core rotation profile of the Sun and other main-sequence solar-type stars remains an enigma. This is due to the absence of detection of gravity modes (g modes) driven by buoyancy, which are evanescent in convective regions, and therefore have very low-amplitude at the surface of main-sequence solar-type stars. Nevertheless, large-scale photometric surveys of these past years have been able to provide us valuable insights on the rotational dynamics of the surface and the upper regions of the stars, thanks to acoustic mode (p modes) asteroseismology and/or the characterisation of photospheric active regions. The upcoming PLATO mission will bring new observational perspectives to constrain these different aspects.
In this seminar, I will first present the possibilities offered by space-based photometry in order to measure surface rotation in large samples of solar-type stars and constrain the dynamics of their convective envelope. In particular, I will describe the machine learning methodology ROOSTER that I developed and the way it will be implemented in the PLATO standard pipeline to monitor stellar rotation and activity. After having presented which yield we can expect from PLATO in terms of stellar rotation and activity characterisation, I will explain how the physically-motivated modelling of stellar active regions (spot modelling) may be connected to low-frequency magneto-inertial waves propagating in the convective envelope. In order to probe stellar internal dynamics and related deep transport processes, I will then discuss the perspective of detecting g modes excited by convective motions in late F-type stars, which are solar-type pulsators with a shallow convective envelope. To this purpose, I used the ASH code to perform several deep-shell 3D hydrodynamic simulations of a 1.3 Msun late F-type star. When describing these simulations, I will highlight the influence of rotation on the increased excitation of the g modes. I will finally present possible evidence of g-mode signature detected in the periodogram of late F-type stars observed by the Kepler satellite, which could allow us to calibrate stellar evolution models in order to reach the accuracy levels required by the PLATO mission.