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Session 66 - Astrophysical Diagnostics from Polarimetry.
Oral session, Wednesday, June 12
We have used both imaging polarimetry and spectropolarimetry to investigate the evolutionary process by which stars similar to the Sun expel their outer envelopes and create planetary nebulae. All of the objets that we have studied are in transition from asymptotic giant branch (AGB) star to planetary nebula, and thus represent the early phases of planetary nebula development. Polarimetry provides a unique tool to probe these early stages of the planetary nebula formation process that are difficult to study using other ground-based techniques. We have used optical spectropolarimetry to look for asymmetry in AGB and post-AGB stars. These objects are too spatially compact to resolve using traditional ground-based imaging techniques. Our results indicate that aspherical structure is present in the majority of the objects that we studied. The spectra of some young planetary nebulae are a combination of polarized and unpolarized light. We have used optical spectropolarimetry to separate these two components in three young planetary nebulae and find that shock emission dominates the optical line spectra of these objects. We have used optical and near-IR imaging polarimetry to investigate the dust distributions and scattering geometries in several young planetary nebulae. We have modeled the polarization vector plots and object morphologies using a Monte Carlo radiative transfer code.
Program listing for Wednesday