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Paper: Near Infrared Imaging Polarimetry of Proto-Planetary Nebula - OH231.8+4.2
Volume: 274, Observed HR Diagrams and Stellar Evolution: The Interplay Between Observational Constraints and Theory
Page: 122
Authors: Ahmad, A.; Gledhill, T.; McCall, A.; Takami, M.
Abstract: Proto-Planetary Nebulae (PPN) are a class of short-lived objects representing a period of around 1000 years of stellar evolution between the Asymptotic Giant Branch and Planetary Nebula phases. This part of the Hertzsprung-Russell diagram is not very well understood from theory although it represents an important phase of low and intermediate mass (0.8 Msun < M < 8 Msun) stellar evolution. We present near infrared (NIR) linear and circular imaging polarimetry of the bipolar outflows of a well studied PPN - OH231.8+4.2 in the J-band (1.2 microns). We detected high linear polarisation (~ 50%) in the lobes of the nebula. We detected a maximum circular polarisation of (~ 1.7%) in the J-band which is probably the first detection in a PPN at NIR wavelengths. We also present results from an optically thick computer model to generate the polarisation patterns from the PPN. From our observations and modelling we conclude that the high levels of NIR linear polarisation seen in the ! bipolar lobes arise from scattering off spherical, Rayleigh-like dust grains and the circular polarisation is generated by multiple scattering, off a small population of spherical, non-Rayleigh dust grains.
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