Diffraction-limited 3 um Spectroscopy of IRAS 04296+3429 and IRAS   05341+0852: Spatial Extent of Hydrocarbon Dust Emission and Dust Evolutionary   Sequence
  We present 3 um spectroscopy of the carbon-rich proto-planetary nebulae IRAS 04296+3429 and IRAS 05341+0852 conducted with the adaptive optics system at the Subaru Telescope. We utilize the nearly diffraction-limited spectroscopy to probe the spatial extent of the hydrocarbon dust emitting zone. We find a hydrocarbon emission core extending up to 100--160 mas from the center of IRAS 04296+3429, corresponding to a physical diameter of 400--640 AU, assuming a distance of 4 kpc. On the other hand, we find that IRAS 05341+0852 is not spatially resolved with this instrumentation. The physical extent of these proto-planetary nebulae, along with the reanalyzed data of IRAS 22272+5435 published previously, suggests a correlation between the physical extent of the hydrocarbon dust emission and the spectral evolution of the aliphatic to aromatic features in these post-AGB stars. These measurements represent the first direct test of the proposed chemical synthesis route of carbonaceous dust in the circumstellar environment of evolved stars. 
M. Goto (1), Sun Kwok (2), H. Takami (3), M. Hayashi (3), W. Gaessler   (1), Y. Hayano (3), M. Iye (4), Y. Kamata (4), T. Ka...