Asymmetry and Inhomogeneity in Proto and Young Planetary Nebulae

I study some effects of aspherical mass loss during the last stages of the asymptotic giant branch (AGB) on the appearance of proto planetary nebulae (PNs) and young PNs. The aspherical mass loss can be small scale inhomogeneities, and/or axially symmetric mass loss geometry. I first examine the role of the dust opacity in the optical band on the appearance of proto-PNs. I conclude that large optical depth will be found in proto-PNs which are descendant of AGB stars having high equatorial mass loss rates, which require a stellar binary companion for their existence. These proto-PNs will become bipolar-PNs, i.e., PNs with two lobes an an equatorial waist between them, or extreme elliptical PNs. I then derive the conditions for the enhancement of non-radial density inhomogeneity by the propagation of the ionization front at the early PN stages. The ionization will proceed faster in the radial direction along low density regions. The low density regions will be heated earlier, and they will expand due to their higher pressures, reducing further their densities. The opposite occurs in high density regions.