The Fast CN Cycle.
Abstract
If temperatures in excess of 100 million degrees occur at the site of hydrogen burning through proton captures by carbon and nitrogen nuclei in a star, the probability is high (Caughlan, G. R., and Fowler, W. A., Astrophys. J. 136, 453, 1962) that N13 will capture a proton in a time short compared to the 867 second p-decay mean lifetime of N13. Thus, under proper temperature and density conditions, one should expect the fast CN cycle C12 (p,7) N13 (p+v) C'0 (p,7) N14 (p,7) 015 (p+v) N15 (p,a) C'2 or N'3(p,7)O'4(p+v) N'4 to be active. We have investigated the mean lifetimes and relative equilibrium abundances of the nuclei of this cycle in the temperature range 50 million to 250 million degrees and the density range 0.1 to 10~ g/cm3. There are substantial differences between the equilibrium abundances of the slow cycle (first line of reactions) and of the fast (combined) cycle. For a given density in the fast CN cycle, at low or at high temperatures in the range investigated, the final ratio of nitrogen to carbon abundances is large, but for an intermediate temperature a minimum of approximately 2 occurs in the nitrogen to carbon ratio. Accompanying this minimum in N/C is a maximum in the ratio of C'3 to C'2 that is greater than one for most density conditions. The results of this investigation and the effects of the fast CN cycle on the cosmic abundances of carbon and nitrogen will be the subj ect of a paper by the present authors in the near future. This work is supported in part by the National Aeronautics and Space Administration under grant NsG-430, and the National Science Foundation under grant number GP-4693.
- Publication:
-
The Astronomical Journal
- Pub Date:
- 1965
- DOI:
- 10.1086/109550
- Bibcode:
- 1965AJ.....70Q.670C