Where is the Doughnut? Luminous Blue Variable Bubbles and Aspherical Fast Winds

In this paper we address the issue of the origin of LBV bipolar bubbles.Previous studies have explained the shapes of LBV nebulae, such as $\eta$ Car,by invoking the interaction of an isotropic fast wind with a previouslydeposited, slow aspherical wind (a ``slow torus''). In this paper we focus onthe opposite scenario where an aspherical fast wind expands into a previouslydeposited isotropic slow wind. Using high resolution hydrodynamic simulations,which include the effects of radiative cooling, we have completed a series ofnumerical experiments to test if and how aspherical fast winds effect windblown bubble morphologies. Our experiments explore a variety of models for thelatitudinal variations of fast wind flow parameters. The simulationsdemonstrate that aspherical fast winds can produce strongly bipolar outflows.In addition the properties of outflows recover some important aspects of LBVbubbles which the previous "slow torus" models can not.Comment: 23 pages, 6 figures, to appear the Astrophysical Journa