next up previous contents index
Next: Nomenclature Up: ``Ecology'' of Magnetic Rotators Previous: Effect of the Magnetic

The Corotation Radius


The corotation radius is another important characteristic of a magnetic rotator. Suppose that an accreting plasma penetrates the light cylinder and is stopped by the magnetic field  at a certain distance tex2html_wrap_inline9547 given by the balance between the static magnetic field pressure and the plasma pressure. Suppose that the plasma is ``frozen'' in the rotator's magnetic field. This field will drag the plasma and force it to rotate rigidly with the angular velocity of the star. The matter will fall on to the stellar surface only if its rotational velocity is smaller than the Keplerian velocity  at the given distance tex2html_wrap_inline9547 :


Otherwise, a centrifugal barrier emerges and the rapidly rotating magnetic field impedes the accretion of matter (Schwartzman, 1970a[173]; Pringle and Rees, 1972[164]; Davidson and Ostriker, 1973[38]; Lamb et al., 1973[93]; Illarionov and Sunyaev, 1975[76]). The latter authors assumed that if tex2html_wrap_inline9572 , the magnetic field throws the plasma back beyond the capture radius. They called this effect the ``propeller''  regime. In fact, matter may not be shed (Lipunov 1980, 1982d[97, 101]), but it is important to note that a stationary accretion  is also not possible.

The corotation radius is thus defined as


where P is the rotational period of the star.

If tex2html_wrap_inline9576 , rotation influences the accretion insignificantly. Otherwise, a stationary accretion  is not possible for tex2html_wrap_inline9578 .

Mike E. Prokhorov
Sat Feb 22 18:38:13 MSK 1997