Where is the doughnut? Luminous blue variable bubbles and aspherical fast winds

Abstract

In this paper, we address the issue of the origin of luminous blue variable (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 previously deposited, slow aspherical wind (a "slow torus"). In this paper we focus on the opposite scenario in which an aspherical fast wind expands into a previously deposited isotropic slow wind. Using high-resolution hydrodynamic simulations, which include the effects of radiative cooling, we have completed a series of numerical experiments to test if and how aspherical fast winds effect wind-blown bubble morphologies. Our experiments explore a variety of models for the latitudinal variations of fast wind flow parameters. The simulations demonstrate that aspherical fast winds can produce strongly bipolar outflows. In addition, the properties of outflows recover some important aspects of LBV bubbles that the previous slow torus models cannot