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Sakurai’s Object, V605 Aql and FG Sge: An Evolutionary Sequence Revealed

Published online by Cambridge University Press:  12 April 2016

Timothy M. Lawlor  and
James MacDonald
Timothy M. Lawlor
Affiliation:
Pennsylvania State University - Wilkes Barre, Lehman, PA 18627, USA
James MacDonald
Affiliation:
University of Delaware, Newark, DE 19716, USA

Abstract

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We have completed a grid of stellar evolution calculations to study the behavior of the born again phenomenon. All our evolutionary sequences begin with a uniform composition 1 M⊙ star on the pre-main sequence Hayashi phase and end on the white dwarf cooling track. We find a very late thermal pulse occurs in 10 – 15 percent of cases. Our models supply an answer to the question of why the born again stars V4334 Sgr (Sakurai’s Object) and V605 Aql have a significantly shorter evolutionary time scale than the otherwise similar born again star FG Sge. Models with low convective mixing efficiency, η = 10–4, first evolve quickly to the AGB, return to the blue, and then evolve more slowly back to the AGB for a second time before finally returning to the white dwarf cooling track. The difference in evolution time scales can then be explained by proposing that Sakurai’s Object is evolving to the AGB for the first time but FG Sge has been observed during its second return to the AGB.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 187: Exotic Stars as Challenges to Evolution , 2002 , pp. 193 - 199
Copyright
Copyright © Astronomical Society of the Pacific 2002

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