par Masao Takata (University of Tokyo)
Résumé :
Asteroseismology is a subfield of stellar astrophysics that aims to diagnose the internal structure and dynamics of stars by measuring their oscillations at the surface. This area of study has recently seen significant development thanks to space missions such as CoRoT, Kepler and TESS. This trend is set to accelerate further with the forthcoming PLATO mission. Of the many successful examples, I will discuss one particular object: KIC 9244992, an F-type main-sequence star observed by the Kepler space telescope. This star exhibits two types of oscillation: short-period (high-frequency) oscillations with the periods of a few hours and long-period (low-frequency) oscillations with the periods of about a day. This classification places the star in the category of delta Sct–gamma Dor hybrid pulsators. The most remarkable finding is that the rotational triplet structure has been clearly detected in both frequency domains, enabling us to constrain the rotation structure in both the core and the envelope. Furthermore, by carefully examining the fine structure (i.e. asymmetry) of the triplet in the low-frequency domain, we can successfully identify the signature of the internal magnetic field and constrain its strength and geometry. We discuss the possible origins of the field and the implications of these findings.
Lieu : salle 1-2-3, bât.121