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M. Morris (UCLA), R. Sahai (JPL/Caltech)
The JPL/MIRLIN camera has been used on the Keck II Telescope to begin a study of pre-planetary nebulae (PPNe) and very young planetary nebulae at mid-infrared wavelengths. This study enables us to probe the inner regions of these objects, such as the high extinction dust toroids which often surround the central stars. Our study thus complements ongoing imaging studies with the Hubble Space Telescope (HST) which operates at shorter wavelengths, and are thus most sensitive to scattered light arising in nebular regions of lower extinction. With observations at both 8.8 and 20.8~\micron~wavelength, the Keck resolution approached the telescope's diffraction limit (0.4" and 0.6", respectively).
Two PPNe were observed in June 1998: CRL2688 and IRAS22272+5435. Considerable structure was observed in the polar lobes of CRL2688, and the 20.8~\micron~observation revealed for the first time thermal emission from the equatorial dust cocoon. Comparison with recent HST images of this source (Sahai et al. 1998a,b) clarifies the location of the dust and strengthens the case for the presence of a companion star located off the symmetry axis of the system. IRAS22272+5435 is resolved for the first time at mid-infrared wavelengths into a roughly ring-like structure centered on the central star. During 1998 October, further observations were carried out of IRAS20028+3910, IRAS22574+6609, and IRAS23304+6147 in marginal weather conditions. The consequent useful constraints on the morphology of these PPNe will be presented.
\vspace{0.2in} \noindent References
\noindent Sahai, R. et al. 1998a, ApJ, 492, L163
\noindent Sahai, R. et al. 1998b, 1998b, ApJ, 493, 301
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