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Session 81 - Planetary Nebulae.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We present optical imaging and imaging polarimetry of three young bipolar planetary nebulae: GL 618, M1-92, and M1-91. We have obtained images of M1-92 and GL 618 through filters centered on [S II] \lambda6717,31 and [O I] \lambda6300. These images trace the distribution of shock heated gas in these objects. We find that the shock emission is concentrated in diffuse peaks in the bipolar lobes of GL 618 and M1-92. This shock emission may trace a weakly collimated outflow or be related to the FLIER's seen in more evolved planetary nebulae.
We have used our optical polarization maps to study the dust distributions and scattering geometries in GL 618, M1-92, and M1-91. The imaging polarimetry was obtained using the new dual-beam imaging polarimeter on the McDonald Observatory 2.1m telescope. We have used a Monte Carlo radiative transfer code, which includes the effects of multiple scattering, to model the polarization seen in these nebulae. We find that the simple dust distributions proposed previously for this type of object cannot account for the observed polarization characteristics of these three objects. We have adopted new a dust distribution in which the lobes are modeled as cavities surrounded by a cylindrical dust envelope. These new models can reproduce the observed polarization maps.
\vspace20pt This work was supported by NSF Grant 91-15101. SRT is currently supported as a Grainger Postdoctoral Research Fellow at the University of Chicago.
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