{'fraction_non_alphanumeric': 0.025233644859813085, 'fraction_numerical': 0.0, 'mean_word_length': 5.12, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Understanding the immediate progenitors of planetary nebulae

Abstract Pre-Planetary Nebulae (PPNe) are believed to represent a relatively short, intermediate evolutionary phase in the evolution of AGB stars to Planetary Nebulae (PNe). Our unbiased, high-resolution imaging surveys with HST of young PNe and PPNe show very strong morphological similarities between these classes, enabling us to extend our morphological scheme for PPN classification to young PNe, preserving virtually all of the primary and secondary descriptors, and adding a few new ones. These morphological surveys show that the primary shaping of PNe begins during the PPNe and/or late-AGB phase, and the key to understanding the shaping process lies in the study of these PNe progenitors. Here we present results from two recent studies of PNe progenitors: (i) Hα emission with very broad wings and P-Cygni profiles as probes of the region where the fast post-AGB outflows that do the shaping are most likely launched from, and (ii) equatorial waists with large-sized dust grains and large masses.