RESEARCH
RESEARCH
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Solar / Stellar / Planetary physics
Solar / Stellar / Planetary physics
Theory of stellar/planetary property is one of the cornerstones in our understanding of the universe. While the conventional approach has been fairly successful in describing the global picture of stellar evolution, there still remain some important questions. I am dealing with some remained problems, conducting analytical calculations, numerical simulations, and observations.
Asteroseismology
Asteroseismology is the field to study stellar internal structures by using surface oscillations of stars. Thanks to space telescopes missions (e.g. Kepler), our understanding about star interiors is proceeded. However, there are many phenomena that cannot be interpreted by the recent stellar physics.
We have theoretically investigated the newly discovered phenomenon, resonance between the inner core and the outer layer in the oscillations of γ Doradus stars, a fast rotating 1.2-1.8 solar mass star (Tokuno & Takata 2022).
Spin Evolution of Low-mass Stars
The angular momentum transport of magnetized stellar winds spins down cool stars, including the Sun (magnetic braking). The spin-down of cool stars exhibits the complicated behavior and its physical interpretation is actively discussed.
We proposed a simple model to track the spin-down of solar-type stars that takes into account differential rotation and discussed its properties (Tokuno, Suzuki & Shoda 2023).
Tidai Evolution of Exoplanetary System
Tidal interactions are thought to play an important role in the orbital evolution of planets. However, the specific mechanisms and efficiency of tidal interactions are still unclear.
We has proposed a novel method for determining the upper limit of the efficiency of tidal interactions in a system of low-mass stars and orbiting gas planets by applying the mathematical field of dynamical systems (Tokuno, Fukui & Suzuki 2024).
Magnetic Activity of the Sun / Solar-type Stars
Surface magnetic activity such as spots and flares is key to characterizing the Sun and understanding its impact on planetary environments. Some solar-type stars show much stronger activity, and comparing them with the Sun helps build a unified picture of stellar magnetism.
We has investigated the temporal evolution of flare frequencies via spot evolution in the Sun and solar-type stars. We show the similar patterns regardless of spot size or flare energy, which suggests common underlying processes (Tokuno, Namekata, Maehara, Toriumi 2025).
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