Magnetic-Driven Winds from Post-AGB Stars: Solutions for High Speed Winds and Extreme Collimation

摘要

This paper explores the effects of post-AGB winds driven solely by magneticpressure from the stellar surface. It is found that winds can reach high speedsunder this assumption, and lead to the formation of highly collimatedproto-planetary nebulae. Bipolar knotty jets with periodic features andconstant velocity are well reproduced by the models. Several wind models withterminal velocities from a few tens of $kms$ up to $10^3$ $kms$ arecalculated, yielding outflows with linear momenta in the range $10^{36}-10^{40}gcms$, and kinetic energies in the range $10^{42}-10^{47} $ erg. These resultsare in accord with recent observations of proto-planetary nebulae that havepointed out serious energy and momentum deficits if radiation pressure isconsidered as the only driver for these outflows. Our models strengthen thenotion that the large mass-loss rates of post-AGB stars, together with theshort transition times from the late AGB to the planetary nebula stage, couldbe directly linked with the generation of strong magnetic fields during thistransition stage.