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Inferring past accretion bursts from asteroseismic imprints

Sede A. Riccò Via Santa Sofia 78, Catania

Stars form during the collapse of dense molecular cloud cores. However, most of their final mass comes from the ensuing protostellar disk, owing to non-zero angular momentum in the cloud. Here, the protostar gains up to 50% of its final mass in episodic bursts of mass accretion, while having quiescent phases between the bursts. In this presentation I present a study of how the occurrence of such bursts may be inferred using asteroseismology - the study of stellar pulsations. Specifically, I show how these intense episodes leave a detectable asteroseismic imprint in the deep stellar interior.

The EWOCS view of supermassive stellar clusters

Sede A. Riccò Via Santa Sofia 78, Catania

Star formation in our Galaxy typically occurs in environments less massive than 10^4 solar masses. However, a few more extreme star forming environments on the Milky Way exist, where hundreds of thousands to millions of stars form in dense regions. Often called “supermassive star clusters”, they are rare in our Galaxy today, while they are common in galaxies experiencing epochs of starburst. The international project EWOCS (Extendend Westerlund 1 and 2 Open Clusters Survey) is targeting the two closest superstar clusters in the Milky Way with a multi-wavelengtht survey which is based on an extensive set of data from radio to X-rays, with the main objective of studying the formation and early evolution of stars over the whole mass spectrum in a starburst environment.
In this talk, I will discuss the motivations and objectives of the project, the published results, ongoing studies and the future developments.

Magnetic instabilities and angular momentum transport in red giant core

Sede A. Riccò Via Santa Sofia 78, Catania

The stability of magnetic fields in radiative stellar interiors remains a fundamental open question in understanding the rotational and chemical evolution of low-mass stars. Recent high-resolution asteroseismic observations of red giants have revealed unexpectedly slow core rotations and the presence of strong internal magnetic fields, opening a new window on the internal dynamics of evolved stars. In this talk, I will review the main magnetohydrodynamic instabilities expected in radiative stellar interiors and present new 3D direct numerical simulations of the Tayler instability, a kink-type instability of toroidal magnetic fields prevalent in these regions. By combining simulations, linear stability analysis, and stellar evolution models, we identify where and under what conditions the Tayler instability is likely to operate in red giant cores. These results provide new insight into angular momentum transport in evolved low-mass stars and may also have broader implications for other stars with radiative interiors.