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|Title:||The Evolution of Planetary Nebula Nuclei|
|Author(s):||Shaw, Richard Allen|
|Department / Program:||Astronomy|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Astronomy and Astrophysics|
|Abstract:||The evolution of planetary nebula nuclei (PNNs) is examined with the aid of the most recent available stellar evolution calculations and new observations of these objects. Their expected distribution in the log L-log T plane is calculated based upon the stellar evolutionary models of Paczynski, Schonberner and Iben, the initial mass function derived by Miller and Scalo, and various assumptions concerning mass loss during post-main sequence evolution. The distribution is found to be insensitive both to the assumed range of main-sequence progenitor mass and to reasonable variations in the age and the star forming history of the galactic disk. Rather the distribution is determined by the strong dependence of the rate of stellar evolution upon core mass, the steepness of the initial mass function, and to a lesser extent the finite lifetime of an observable planetary nebula. The theoretical distributions are rather different than any of those inferred from earlier observations. Possible observational selection effects that may be responsible are examined, as well as the intrinsic uncertainties associated with the theoretical model predictions.
An extensive photometric and smaller photographic survey of southern hemisphere planetary nebulae (PNs) is presented. Seven new PNs were discovered in or near Baade's Window, and total fluxes in several nebular lines, relative to H(beta), are presented for 134 southern PNs. New B and/or V magnitudes for the nuclei of 117 PNs are presented, and are combined with 54 magnitudes (as well as limits for ten others) from absolute photometry of northern PNNs. We develop a superior method of extracting stellar continuum fluxes from a bright nebular background, and carefully examine the errors and limitations of the method.
The continuum measurements are compared with the widely circulated list of preliminary central star magnitudes by Shao and Liller, which are shown to suffer frequently from severe contamination from the nebular continuum. A calibration for older photographic magnitudes is determined, and the effect of the nebular contamination of the stellar continuum for luminous objects on the study of the evolution of PNNs is examined.
The temperatures and luminosities are derived for nearly all of the PNNs in this sample via the Zanstra and Shklovsky methods. The observed log L-log T distribution of PNNs is presented, and large discrepancies with the theoretical distributions are examined. In particular, the Zanstra technique is found to be unable to yield stellar temperatures much hotter than log T (TURN) 5.1. This limitation and the effects of stellar winds and an uncertain distance scale upon the study of PNN evolution are evaluated and discussed.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
|Date Available in IDEALS:||2014-12-16|