Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-11-23
Astronomy and Astrophysics
Astrophysics
5 pages, 2 figures, emulapj.sty Replace: new Figure 2
Scientific paper
10.1086/306945
A model is developed for magnetic `propeller'-driven outflows which cause a rapidly rotating magnetized star accreting from a disk to spin-down. Energy and angular momentum lost by the star goes into expelling most of the accreting disk matter. The theory gives an expression for the effective Alfven radius $R_A$ (where the inflowing matter is effectively stopped) which depends on the mass accretion rate, the star's mass and magnetic moment, and the star's rotation rate. The model points to a mechanism for `jumps' between spin-down and spin-up evolution and for the reverse transition, which are changes between two possible equilibrium configurations of the system. In for example the transistion from spin-down to spin-up states the Alfven radius $R_A$ decreases from a value larger than the corotation radius to one which is smaller. In this transistion the `propeller' goes from being ``on'' to being ``off.'' The ratio of the spin-down to spin-up torque (or the ratio for the reverse change) in a jump is shown to be of order unity.
Bisnovatyi-Kogan Gennadi S.
Lovelace Richard V. E.
Romanova Marina M.
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