Studying the Effects of Light Echoes Around Evolved Stars

Abstract

There is much still to be understood about stars in the late stages of stellar evolution, including the processes that induce and shape the material they eject. For solar mass stars, ejecta expelled in the AGB phase form planetary nebulae, thus understanding planetary nebulae will help us understand the stars. Light echoes have already been used to determine the characteristics of much larger nebulous objects.A project was devised with the aim of investigating three different evolved stars, each accociated with a nebulosity, specifically to see if light echoes could be used to determine any of their characteristics. This was to be done with the aid of a program called `Shape', a program used to model and analyse nebulae in 3D, which contained a newly introduced light echo feature. Observational data of RZ Sgr, a Mira variable surrounded by a visible reflection nebula, was compared with simulated echo structures in the aim of identifying the existence of echoes. Light curves were then simulated for the nebulosity observed surrounding CK Vul, to see if they could explain the strange profile due to its 1670 nova event. Images of V458 Vul (a planetary nebula undergoing flash ionisation due to a recent nova event) were used to construct a model in the aim of constraining some of its characteristics.Hints of the existence of light echoes around RZ Sgr were found which could consequently be used to identify its orientation - results which were dependant on the chosen representative structure. Explaining CK Vul's observed profile through a light echo was found to be unlikely. A novel method was devised to determine an accurate distance for V458 Vul. With the available data, a range of 5 - 6.5 kpc was estimated, but the options for extending the upper limit of these estimates is discussed.It is concluded that light echoes are a useful tool in determining characteristics of planetary nebulae and similarly sized nebulous objects, specifically their distance, orientation and 3D structure.This thesis, entitled `Studying the Effects of Light Echoes Around Evolved Stars', was submitted by Peter Gordon to the University of Manchester for the degree of Master of Science on Friday 3rd September 2010.

Date of Award	31 Dec 2010
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Albert Zijlstra (Supervisor)