3D MHD simulations of an accreting young star

Young stars such as protostars and pre-main-sequence stars evolve via the interaction with the surrounding accretion disks. It is believed that stellar and disk magnetic fields play important roles in shaping the accretion structure and exchanging the angular momentum between the stars and the disks. However, because of the complexity of gas dynamics around the stars, the star-disk interaction remains poorly understood, which makes the construction of the stellar evolution models difficult. To reveal the interaction processes, we have been performing 3D magnetohydrodynamic simulations of accretion onto a young star with different stellar magnetic fields. In the case of a weakly magnetized, magnetosphere-free star, we found that failed disk wind becomes supersonic, high-latitude accretion flows onto the star (Takasao et al. 2018). This result may explain the reason why Herbig Ae/Be stars show fast accretion. In a different model with stronger disk fields, we showed that the star can produce recurrent explosions via magnetic reconnection (Takasao et al. 2019). We consider that the mechanism is relevant to protostellar flares in class-0/I protostars. In addition to the above two models, we have been investigating the magnetospheric accretion which is very relevant to classical T-Tauri stars. In this talk, we will introduce our 3D modeling and discuss how the star-disk interaction changes depending on the stellar and disk field strengths.