Flaring activity on the disk of Classical T Tauri Stars: effects on disk stability

Abstract

Classical T Tauri Stars (CTTSs) are young stellar objects surrounded by a circumstellar disk with which they exchange mass and angular momentum through accretion. Despite this process is a crucial aspect of star formation, some issues are still not clear; in particular how the material loses angular momentum and falls into the star. CTTSs are also characterized by strong X-ray emission. Part of this X-ray emission comes from the heated plasma in the external regions of the stellar corona with temperature between 1 and 100 MK. The plasma heating is presumably due to the strong magnetic field (Feigelson and Montmerle, 1999) in the form of high energetic flares in proximity of the stellar surface. This energetic phenomena may influence the circumstellar environment. Recently, Reale et al. (2018) proved that long flares may connect the disk to the stellar surface. Moreover a study of Orlando et al. (2011) has shown that an intense flare close to the disk may strongly perturb its stability, inducing accretion episodes. Starting from these lines of evidence, here we investigate the effects of multiple flares with low-to-medium intensity on the disk stability, and check if they may be responsible for triggering accretion episodes. To this end, we developed a 3D magnetohydrodynamics model describing a CTTS surrounded by an accretion disk subject to intense flaring activity. The flares occur randomly in proximity of a thick disk. We found that the flaring activity determines the formation of a hot extended corona that links the disk to the stellar surface. In addition, the flares strongly perturb the disk and trigger accretion phenomena with a mass accretion rate comparable with those inferred by X-ray observations.