PI: Toshiya Ueta, University of Denver, email@example.com
Address: Physics Department, 2112 E. Wesley Ave, Denver, CO 80208, USA
Title: Probing of the Structure of Optically-Thin Proto-Planetary Nebulae with Angular Differential Imaging
Abstract: We propose to resolve the structure of 6 optically-thin proto- planetary nebula (PPN) dust shells by means of angular differential imaging using NICI at Gemini-South. According to our previous imaging surveys using the Hubble Space Telescope, these PPNs show a compact elliptical nebulosity (of radius 0\farcs5 to 2\arcsec) with a prominently visible central star. These PPNs appear to be members of a distinct class of PPNs, compared with bipolar nebulae in which an optically thick dust lane obscures the central star. Based on our previous mid-IR PPN survey, these PPNs host an optically thin, toroidal dust shell as evidence for their intrinsic axisymmetry supposedly caused by an equatorially-enhanced mass loss during late stages of the asymptotic giant branch phase. While we performed imaging-polarimetry to isolate dust-scattered, polarized light arising from the shell, the bright central star still left enormous imprints that prevented us from investigating shell structures within 1^\prime\prime to the central star. The unique ability of angular differential imaging available at NICI makes Gemini-South the only telescope capable of recovering the structure of compact PPNs by reducing further the effects of the enormous PSF structure of the dominantly bright central star. These observations and following analysis with our radiative transfer code will provide crucial clues to the physical mechanism that drives the axisymmetric mass loss from originally spherically symmetric stars, which still remains to be one of the fundamental problems in astrophysics.
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