• Schmidt, G. D.
• Bieging, J. H.
• Oppenheimer, B. D.
• Misselt, K. A.
• Gordon, Karl

Abstract

We have used the Steward Observatory 2.3 m telescope with the SPECPOL spectropolarimeter to observe selected AGB and post-AGB stars (including R CrB) and several proto-planetary nebulae (PPNe). The spectra cover 4500 - 8500Å with 13Å resolution, in total and linearly polarized flux, and position angle of linear polarization. Multi-epoch observations of several objects show variability in the polarized spectra. Spectra near maximum and minimum light for the AGB stars imply significant changes in the dust envelopes over the light cycle. R CrB was observed at normal intensity and near a deep minimum, with very different polarized spectra at the two epochs. To interpret these data, we use the Monte Carlo dust scattering code of Gordon, Misselt, et al. (2001, ApJ, 551, 269; 551, 277) to model aspects of the observed polarized spectra. A range of grain sizes and compositions (graphite, amorphous carbon, or silicates) are used in the models. We present preliminary results of models for the PPNe assuming axisymmetric dust distributions, also using constraints from other observations, e.g., high resolution images and integrated spectral energy distributions. We discuss the constraints on the dust distributions, compositions, and grain sizes set by comparison of these models with our spectropolarimetry data. This work is supported by National Science Foundation grant AST99-87408 to the University of Arizona.

Topics

• impedance spectroscopy
• amorphous
• Carbon
• grain
• grain size