[Previous] | [Session 44] | [Next]
E. Blackman, A. Frank, C. Welch (University of Rochester)
MHD winds can emanate from stars and surrounding discs. When the two systems are coupled by accretion, it is important to know which (if either) of the two dominates the outflow power. In the context of planetary nebulae (PN), we calculate the power of coupled disc and stellar winds for the cases of an initially rapidly spinning and initially slowly spinning central star, and show that the results depend only on the accretion rate and stellar properties.
For times greater than a spin-down time, the central post AGB stellar envelope/shell is slaved to the disc for both cases and the disc wind luminosity dominates. If the shell were initially slowly rotating, the disc wind would dominate throughout the evolution. In the rapidly rotating case, the stellar wind can be initially of comparable power to the disc wind. The two remain comparable for a few years, with the decreasing accretion rate depleting the disc wind more quickly than the stellar wind, until the spin down time of the stellar shell is reached and the disc wind dominates. Since an initially independently rapidly rotating star can have its spin and magnetic axes misaligned to the disc, multipolar outflows can result from the disc wind system.