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We present a semi-analytic model for shaping the nebula around eta Carinaethat accounts for the simultaneous production of bipolar lobes and anequatorial disk through a rotating surface explosion. Material is launchednormal to the surface of an oblate rotating star with an initial kick velocitythat scales approximately with the local escape speed. Thereafter, ejectafollow ballistic orbital trajectories, feeling only a central forcecorresponding to a radiatively reduced gravity. Our model is conceptuallysimilar to the wind-compressed disk model of Bjorkman & Cassinelli, but wemodify it to an explosion instead of a steady line-driven wind, we include arotationally-distorted star, and we treat the dynamics somewhat differently.Continuum-driving avoids the disk inhibition that normally operates inline-driven winds. Our model provides a simple method by which rotating hotstars can simultaneously produce intrinsically bipolar and equatorial massejections, without an aspherical environment or magnetic fields. Althoughmotivated by eta Carinae, the model may have generic application to other LBVs,B[e] stars, or SN1987A's nebula. When near-Eddington radiative driving is lessinfluential, our model generalizes to produce bipolar morphologies withoutdisks, as seen in many PNe.

The Structure of the Homunculus. III. Forming a Disk and Bipolar Lobes in a Rotating Surface Explosion