MHD Disk Winds in PNe and pPNe

Winds from accretion disks have been proposed as the driving source for precessing jets and extreme bipolar morphologies in Planetary Nebulae (PNe) and proto-PNe (pPNe). Here we apply MHD disk wind models to PNe and pPNe by estimating separately the asymptotic MHD wind velocities and mass loss rates. We show that the resulting winds can recover the observed momentum and energy input rates for PNe and pPNe. Introduction While considerable progress has been made in understanding the hydrodynamic shaping of elliptical and bilobed PNe (Balick & Frank 2002), the origin of extreme butterfly nebulae as well as jets in PNe continues to pose a number of problems for theorists. In particular a formidable problem for pPNe concerns the total momentum and energy in the outflows. A number of observational studies have shown that radiatively accelerated winds in pPNe cannot account for the high momentum and energy implied by CO profiles (Bujarrabal et al.2001). Thus the total flow momentum Π is such that Π >> (L∗/c)∆t, where L∗ is the stellar luminosity emitted during the pPNe outflow expansion lifetime ∆t. In light of these results both the launching and collimation of winds in pPNe becomes problematic. Note that while both the dominant hydrodynamic theory for shaping PNe, (the Generalized Interacting Stellar Winds model: Balick 1987; Icke 1988), and models invoking an initially weak toroidal magnetic field (Garcia-Segura et al.1999) can produce jets neither can account for the momentum excesses in pPNe. Thus there remains considerable uncertainty about the processes which produce collimated jets/outflows in pPNe and PNe. Other systems which produce jets such as YSOs, AGN and micro-quasars have been modelled via a combination of magnetic and centrifugal forces from accretion disks (Konigl & Pudritz 2000). The success of these Magneto-centrifugal Launching (MCL) models is such that it is worthwhile considering if such a scenario can be applied to PNe and pPNe. While models such as Morris 1987, Soker & Livio 1994 and Soker & Rapport 2001 have relied heavily on collimated winds from disks these works did not specify how such winds are launched or collimated. Thus application of MCL disk wind models to PNe and pPNe would close an important gap in building a new MHD disk wind paradigm for these systems (Blackman, Welch & Frank (2001): BFW01, Blackman et al. 2001). Here we summarize new calculations from Frank & Blackman 2004 who derive scaling relations from the equations for MCL and separately estimate