Rachel Deacon (Sydney University)

Behind the Shaping of Planetary Nebulae - Rachel Deacon Colloquium

ATNF Marsfield Lecture Theatre

Abstract

A significant unsolved problem in low- to medium-mass stellar evolution is the cause of the variation in planetary nebulae (PN) morphologies. Around 50% of observed PN have non-spherical morphologies, whereas it is observed that their stellar progenitors are largely spherically symmetric. The likely contributors to the difference in morphologies include the influence of stellar magnetic fields and companion stars or planets, or some combination of both. The physical parameters of the central star also play a role. For example, the most bipolar PN belong to a more massive population of stars.

For my PhD I have studied a new sample of 85 post-Asymptotic Giant Branch (post-AGB) candidates, the precursor stars to PN. Post-AGB stars have migrated off the AGB and the mass-loss phase, but are not yet fully-ionised PN. These stars are difficult to investigate as they are short-lived and therefore rare, and are usually not optically visible as they are surrounded by thick dust shells. This sample was selected from a Galactic OH 1612 MHz maser survey according to the stars' infrared colours. Younger, older, low-mass and high-mass subsets were identified. In this colloquium, I will present the results of my PhD thesis.