Asteroseismic modelling of fast rotators and its opportunities for astrophysics

Abstract

Rotation matters for the life of a star. It causes a multitude of dynamical phenomena in the stellar interior during a star’s evolution, and its effects accumulate until the star dies. All stars rotate at some level, but most of those born with a mass higher than 1.3 times the mass of the Sun rotate rapidly during more than 90% of their nuclear lifetime. Internal rotation guides the angular momentum and chemical element transport throughout the stellar interior. These transport processes change over time as the star evolves. The cumulative effects of stellar rotation and its induced transport processes determine the helium content of the core by the time it exhausts its hydrogen isotopes. The amount of helium at that stage also guides the heavy element yields by the end of the star’s life. A proper theory of stellar evolution and any realistic models for the chemical enrichment of galaxies must be based on observational calibrations of stellar rotation and of the induced transport processes. In the last few years, asteroseismology offers such calibrations for single and binary stars. We review the current status of asteroseismic modelling of rotating stars for different stellar mass regimes in an accessible way for the non-expert. While doing so, we describe exciting opportunities sparked by asteroseismology for various domains in astrophysics, touching upon topics such as exoplanetary science, galactic structure and evolution, and gravitational wave physics to mention just a few. Along the way we provide ample sneak-previews for future ‘industrialised’ applications of asteroseismology to slow and rapid rotators from the exploitation of combined Kepler, Transiting Exoplanet Survey Satellite (TESS), PLAnetary Transits and Oscillations of stars (PLATO), Gaia, and ground-based spectroscopic and multi-colour photometric surveys. We end the review with a list of takeaway messages and achievements of asteroseismology that are of relevance for many fields of astrophysics.