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Nova Modeling

Published online by Cambridge University Press:  30 March 2016

Warren M. Sparks ,
G. Siegfried Kutter ,
Sumner Starrfield  and
James W. Truran
Warren M. Sparks
Affiliation:
NASA/Goddard Space Flight Center, Laboratory for Astronomy and Solar Physics
G. Siegfried Kutter
Affiliation:
NASA/Goddard Space Flight Center, Laboratory for Astronomy and Solar Physics
Sumner Starrfield
Affiliation:
Arizona State University
James W. Truran
Affiliation:
University of Illinois

Extract

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The mass and energy of nova ejecta are 10-5 - 10-4M⊚ and 1044 - 1045 ergs, respectively (Payne-Gaposchkin 1957). Comparison of these quantities with the mass (1 M⊚) and binding energy (1051 erg) of the erupting white dwarf implies that the nova outburst is a surface event. From an average of two or three novae detected each year, it is estimated that the rate of novae is 40-50 per year in our galaxy (Payne-Gaposchkin 1954) . Comparing this rate with a white dwarf birth rate of 2 per year in our galaxy (Weidemann 1968), we conclude that the nova outburst is a recurrent phenomenon (cf. Ford 1978). The recurrent nature also implies that the white dwarf cannot be drastically altered from event to event, thus giving further evidence for a surface event. The argument of recurrency become even stronger when it is realized that observations strongly indicate a close binary structure for the nova candidates—the white dwarf and a red companion (Kraft 1964).

Kraft (1963) proposed the following hypothesis. The red companion overflows its Roche lobe and supplies hydrogen-rich material to an accretion disk around the white dwarf. This material eventually accretes onto the white dwarf, forming an hydrogen-rich envelope whose base is electron-degenerate. As the accretion proceeds, the temperature at the base of this envelope increases. This has little effect on the pressure, but greatly increases the thermonuclear energy generation. The thermonuclear energy generation, in turn, increases the temperature. This positive feedback loop leads to a thermonuclear runaway, which Kraft proposed as the cause of the nova outburst. A large number of theoretical studies based on this model have been carried out. These studies are presented in order of increasing realism and complexity in the following sections.

Type
Joint Discussion
Information
Highlights of Astronomy , Volume 5: Highlights of Astronomy. As presented at the XVIIth General Assembly of the IAU, 1979 , 1980 , pp. 505 - 508
Copyright
Copyright © Cambridge University Press 1980

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