Signatures of wind formation in optical spectra of precursors of planetary nebulae

Generally it is thought that shaping of planetary nebula from initially spherical envelope of asymptotic giant branch stars into non-spherical morphologies is a consequence of binary interactions. However, post asymptotic giant branch stars HD 235858 and HD 161796 seem to be at odds with this idea and perhaps the non-spherical nebulae surrounding them arose from intrinsic change in the nature of the stellar wind which is poorly understood for this evolutionary phase. Spectroscopic monitoring of these two stars has revealed signatures in the spectra that point to variable outflow. This indicates the prospect of spectroscopic monitoring to advance the knowledge of wind launching mechanism in post asymptotic giant branch stars and other dynamical processes in their extended atmospheres.