Nuclear reaction rates and the nova outburst

Abstract

Classical novae participate in the cycle of Galactic chemical evolution in which grains and metal enriched gas in their ejects, supplementing those of supernovae, AGB stars, and WR stars, are a source of heavy elements for the ISM. Once in the diffuse gas, this material is cycled through molecular clouds before being incorporated into young stars and planetary systems during star formation. Infrared observations have confirmed the presence of carbon, SiC, hydrocarbons, and oxygen-rich silicate grains in nova ejects, suggesting that some fraction of the pre-solar grains recently identified in meteoritic material may come from novae. The mean mass returned by a nova outburst to the ISM probably exceeds w 2 x 10-4 M~. Using the observed nova rate of 35+11 per year in our Galaxy, it follows that novae introduce more than N 7 x 10-3 M@ yr-l of processed matter into the ISM. It is likely, however, that novae ejects are more massive than believed, and this value is a lower limit. Novae are expected to be the major source of 15N and 170 in the Galaxy and to contribute to the abundances of other isotopes in this atomic mass range. In order to understand better their contributions to galactic chemical evolution, we have begun a series of studies with the latest nuclear reaction rate libraries. We report both on how these new rates affect the properties of the outburst and, in addition, how they change the predictions of the contributions of novae to Galactic chemical evolution.

Synthesis of Intermediate‐Mass Elements in Classical Novae: From Si to Ca

“…In fact, the reduction of the proton capture rate halts significantly the synthesis of elements above Si (by a factor of ∼ 10 with respect to the values found with the nominal rate). We have compared our results with the latest available results from hydrodynamic simulations of ONe novae by Starrfield et al (2001): they state that the switch to an updated nuclear network (Iliadis et al 2001) is accompanied by an important reduction of the abundances of nuclei above aluminum, in good agreement with the results found here. However, our new computations show that reduction of the yields affect only nuclei above 32 S. In fact, a significant reduction of 32 S results only when we adopt the low 30 P(p,γ) test rate.…”

“…Hence, this discrepancy might be likely attributed to a different prescription for the adopted 30 P(p,γ) rate. In particular, the rate used by Starrfield et al (2001) seems to be somewhat lower than the nominal rate adopted in our paper, which stresses again the crucial dependence of the S-Ca yields on this particular rate.…”

Abundance Analysis of the Extremely Fast ONeMg Novae V838 Herculis and V4160 Sagittarii

“…This range in ejected mass is unexpected if WD mass is the primary controlling variables. However, new theoretical models of Starrfield et al (2000Starrfield et al ( , 2001 and Yaron et al (2005) show that the ejected mass is also dependent on variables such as the initial composition of the accreted shell, the WD temperature, and the accretion rate. Whether the low initial WD luminosities ($10 À3 L ) and mass accretion rates ( 10 À10 M yr À1 ) required by the models is typical for classical nova remains to be seen.…”

THE EFFECTS OF THEpepNUCLEAR REACTION AND OTHER IMPROVEMENTS IN THE NUCLEAR REACTION RATE LIBRARY ON SIMULATIONS OF THE CLASSICAL NOVA OUTBURST

“…A discussion of the improvements is provided in S1998. The third library (labeled I2001) is described in Iliadis et al (2001) and was used for the simulations reported in Starrfield et al (2001). The fourth library (labeled I2005A) is the August 2005 library of Iliadis and the results of calculations done with this library are given in this paper.…”