Disk-Anchored Magnetic Propellers - A Cure for the SW Sex Syndrome

Abstract

In AE Aqr, magnetic fields transfer energy and angular momentum from a rapidly spinning white dwarf to material in the gas stream from the companion star, with the effect of spinning down the white dwarf while flinging the gas stream material out of the binary system. This magnetic propeller produces a host of observable signatures, chief among which are broad single-peaked flaring emission lines with phase-shifted orbital kinematics. SW Sex stars have accretion disks, but also broad single-peaked phase-shifted emission lines similar to those seen in AE Aqr. We propose that a magnetic propeller similar to that which operates in AE Aqr is also at work in SW Sex stars -- and to some extent in all nova-like systems. The propeller is anchored in the inner accretion disk, rather than or in addition to the white dwarf. Energy and angular momentum are thereby extracted from the inner disk and transferred to gas stream material flowing above the disk, which is consequently pitched out of the system. This provides a non-local dissipationless angular momentum extraction mechanism, which should result in cool inner disks with temperature profiles flatter than $T\propto R^{-3/4}$, as observed in eclipse mapping studies of nova-like variables. The disk-anchored magnetic propeller model appears to explain qualitatively most if not all of the peculiar features of the SW Sex syndrome.