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Evolutionary models for SNI progenitor stars

Conference ·
OSTI ID:5026020
Many researchers have proposed that the Type I supernova (SNI) explosion originates in a white dwarf (WD) star that is undergoing mass accretion from a companion star in a close binary orbit. Previous hydrodynamic computations by others have described the final result given the WD mass and composition (usually assumed uniform), the mass accretion rate, and the composition of the accreting matter. Unresolved by these computations, however, are the following questions: (1) how does a given WD evolve to a particular pre-explosion configuration in a realistic scenario; (2) what is the most likely progenitor, hence explosion mechanism; (3) how can an accreting WD ever evolve to a SNI if it first ejects the accreted envelope in one or more nova outbursts; Starrfield, Truran, and Sparks (1981) have proposed, for example, that since at low mass accretion rates, gravitational settling of the CNO nuclei out of the accreted H envelope can occur on the accretion time scale, only steady-state hydrogen burning will occur, leading to no nova outburst. I have performed evolutionary calculations in an attempt to test the Starrfield, et al. suggestion and to clarify these questions. I discuss the details of these calculations, which are based on a variant of the Henyey method, and include the effects of mass accretion, convective mixing, nuclear burning, and gravitational settling. This is the first WD evolutionary calculation that includes all the physical effects thought to be responsible for the composition morphology, while making use of the best available equation of state for WD matter. I present preliminary results of this study, consisting of two evolutionary sequences resulting from spherically symmetric accretion of normal matter (X = 0.700, Y = 0.285) onto an initially pure /sup 12/C WD of mass 1.00 M and initial luminosity given by log L/L = 3.74.
Research Organization:
EG and G, Inc., Los Alamos, NM (USA)
DOE Contract Number:
AC08-76NV01183
OSTI ID:
5026020
Report Number(s):
EGG-1183-1836; CONF-820801-13; ON: DE82019939
Country of Publication:
United States
Language:
English