Name/Affiliation: Marina Romanova (Cornell University)
MHD simulations of magnetospheric accretion, waves in the disk and associated variability
I will discuss results of the global 3D MHD simulations of accretion onto young magnetized stars with a dipole or more complex magnetic fields and will describe properties of the funnel streams and shapes of the hot spots. In the case of a dipole field, the simulations show that magnetized stars may accrete either in a stable regime, where matter flows towards a star in two ordered funnel streams, or in an unstable regime, where matter accretes either in several chaotic "tongues" (which form chaotic spots on the surface of the star), or in 1-2 ordered tongues which rotate with the angular frequency of the inner disk, and therefore their frequency varies with the accretion rate. These regimes of accretion determine the variability patterns of young stars, which range from periodic in the stable regime, to chaotic or quasi-periodic in the unstable regime. A star with a tilted dipole magnetic field excites density and bending waves in the inner disk. The density waves produce density enhancements in the inner disk and may determine position of the funnel streams and unstable tongues. On the other hand, bending waves may be responsible for obscuration of stellar light and AA Tau type light-curves.