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Spectropolarimetry and Radiative Transfer Modeling of Three Proto-Planetary Nebulae
We measured the spectrum of polarization for three proto-planetarynebulae (PPNs), IRAS 17411-2411, IRAS 08005-2356, and IRAS 04296+3429,and made model calculations with the dust-scattering Monte Carlo codeDIRTY and the dust emission code 2Dust. We show that high levels ofpolarization in these PPNs correlate with extreme asymptotic giantbranch (AGB) superwind mass-loss rates in excess of 10-4Msolar yr-1. All three objects show evidence forevacuated lobes cleared by collimated fast winds, and two indicate asignificant equatorial mass enhancement. Our best-fit models requiresharply peaked grain size distributions, suggesting that most of thelight is being scattered by grains of a characteristic size in IRAS17441-2411 and IRAS 08005-2356. IRAS 17441-2411 and IRAS 08005-2356 havelobes with wide opening angles, perhaps produced by deflection of apolar jet from an accreting companion by the AGB superwind. Modeling thespectropolarimetry of IRAS 04296+3429 indicates a point-symmetric,multipolar morphology in the PPN phase. The modeling ofspectropolarimetry and other observations of PPNs provides a powerfulway to constrain circumstellar morphology and dust parameters.
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