The Effects of the pep Nuclear Reaction and Other Improvements in the Nuclear Reaction Rate Library on Simulations of the Classical Nova Outburst
Nova explosions occur on the white dwarf (WD) component of a cataclysmic variable binary stellar system which is accreting matter lost by its companion. When sufficient material has been accreted by the WD, a thermonuclear runaway (TNR) occurs and ejects material in what is observed as a classical nova (CN) explosion. We have continued our studies of TNRs on 1.25 M sun and 1.35 M sun WDs (ONeMg composition) under conditions which produce mass ejection and a rapid increase in the emitted light, by examining the effects of changes in the nuclear reaction rates on both the observable features and the nucleosynthesis during the outburst. In order to improve our calculations over previous work, we have incorporated a modern nuclear reaction network into our one-dimensional, fully implicit, hydrodynamic computer code. We find that the updates in the nuclear reaction rate libraries change the amount of ejected mass, peak luminosity, and the resulting nucleosynthesis. Because the evolutionary sequences on the 1.35 M sun WD reach higher temperatures, the effects of library changes are more important for this mass. In addition, as a result of our improvements, we discovered that the pep reaction (p + e - + p → d + ν) was not included in our previous studies of CN explosions (or to the best of our knowledge those of other investigators). Although the energy production from this reaction is not important in the Sun, the densities in WD envelopes can exceed 104 g cm-3 and the presence of this reaction increases the energy generation during the time that the p-p chain is operating. Since it is only the p-p chain that is operating during most of the accretion phase prior to the final rise to the TNR, the effect of the increased energy generation is to reduce the evolution time to the peak of the TNR and, thereby, the accreted mass as compared to the evolutionary sequences done without this reaction included. As expected from our previous work, the reduction in accreted mass has important consequences on the characteristics of the resulting TNR and is discussed in this paper.