MAGNETIZED ACCRETION AND FUNNEL FLOW

The formation of a standing accretion shock in an axisymmetric, ideal, and steady field-channeled accretion flow (or funnel how) is explored . The shock jump relations are given by the constancy of the integral constants (except the Bernoulli constant as original defined) of magne tohydrodynamic (MHD) equations of the funnel flow across the shock. Th e accretion shock is slow magnetosonic in nature for a sub-Alfvenic fl ow, and it sets a new boundary relating to the inner disk in which the accretion flow is initiated. It is found that if a star is an ideal c onductor, the stellar rotation rate Omega(s) constrains strongly the i ntegral constant alpha of the induction equation and the rotation rate of the inner disk (Omega(d)) in that alpha = Omega(s) and Omega(d) si milar or equal to Omega(s)/(1-D-d), where D-d is the square of the Alf ven Mach number defined by the poloidal magnetic field of the initial funnel flow. Our results can be applied to determine the funnel-associ ated torque on the star. We show that our flow-centered view and the G hosh & Lamb disk centered view lead in general to contradictory result s. In particular, unless the shocked gas has a large deviation from th e stellar rotation, or Delta Omega similar to Omega(s), the funnel flo w could carry only a small portion of angular momentum flux. Since for the shock, Delta Omega = 0 due to the stellar boundary condition for steady accretion, we conclude that the funnel flow transports excess a ngular momentum of the inflowing matter mostly to the disk rather than to the star, a result in accord with the arguments of Shu et al. and the detailed models of Ostriker & Shu. Thus, the matter angular moment um term, as adopted in the Ghosh & Lamb model for the angular momentum accretion, may not exist.