Accretion disc boundary layers in classical T Tauri Stars.
Results of one-dimensional time-dependent calculations of geometrically thin accretion disk boundary layers arc presented for classical T Tauri stars for various values of M* (0.8 and 1.0 M0), R* (1.6, 2.15, and 4.3 R0), and M (5 x 1O- -5 x 1O- M0 ). The results exhibit a thermal boundary layer ( tBhL 0. 1-O.2R *) much larger than the dynamical one ( WL few percent), with characteristic low temperatures ( f 5-6 >c i03 K). In the limit of very low mass accretion rates characteristic of T Tauri systems, the mid-plane temperature in the inner disk drops well below 10 K (a few i03 K at most). A very sharp transition region separates the hot ionized thermal boundary layer region from the cool neutral inner disk. For low values of the viscosity parameter ( 0.01), the medium is optically thin in the cool inner disk and slightly optically thick in the hot thermal boundary layer. This result explains the absence of optically thick material (the "inner hole") as observed in the central part of circumstellar disks around young stellar objects. For higher values of the viscosity parameter ( 0.1), the optical depth in the boundary layer region decreases ( 1) and its temperature increases slightly, while the inner disk becomes partially ionized and optically more thick. Subject headings: accretion, accretion disks stars: formation stars: pre-main-sequence
|Main Author:||Godon, Patrick.|