Young stars such as protostars and pre-main-sequence stars grow through the interaction with the surrounding disks. Since their evolution history and final state depends on the interaction process, it is crucial to reveal the accretion process for understanding the stellar evolution. We have been developing a 3D MHD star-disk model to reveal the accretion process in the vicinity of a central star. In my talk, I will present results of two cases with different disk magnetic field strengths. The weaker and stronger disk field cases will correspond to the systems of a pre-main-sequence star and a protostar, respectively. I will discuss how observational signatures of young stars, such as fast free-falling accretion and flaring activities, are related to MHD dynamics. Regarding the flaring activity, the similarity and difference between solar flares and protostellar flares will also be discussed.

Takasao et al. 2018 ApJ
https://ui.adsabs.harvard.edu/abs/2018ApJ…857….4T/abstract
Takasao et al. 2019, submitted to ApJL (under review)
https://ui.adsabs.harvard.edu/abs/2019arXiv190202007T/abstract