Carbon-nitrogen cycle

The energy of the sun and stars can be attributed at least in part to the well-known carbon-nitrogen cycle. 

CARBON-NITROGEN CYCLE (second- and later-generation stars)... 

The 14N atom is the fourth mostabundantnucleus that is produced by nucleosynthesis in the stars (after l60,12C and 20Ne). Its nucleosynthesis occurs primarily in stars of insufficient mass to become supernovae, especially in AGB stars (see Glossary). It is the natural byproduct of the fusion of hydrogen into helium in the carbon-nitrogen cycle. The 14N is created by proton-capture reactions transmuting the initial C and O within the star to 14N during the CN cycle. Production from intial C and O makes 14N a secondary nucleus, since it can be made only in proportion to the amount of C... 

In addition to the process described in the text, a second process called the carbon—nitrogen cycle occurs in the sun ... 

Walsh et al. (1999) Simulation of carbon/nitrogen cycling during spring upweUing in the Cariaco Basin... 

Walsh, J. J. (1996). Nitrogen fixation within a tropical upweUing ecosystem Evidence for a Redfield budget of carbon/nitrogen cycling by the total phytoplankton community. J. Geophys. Res. 101 (C9), 20607-20616. 

The first stage of nucleogenesis in the stars is the fusion of protons into He by the net reaction (section 8.12, deuteriiun cycle, carbon nitrogen cycle or others)... 

In more massive stars (temperatures of 6 X 10 K or higher), the carbon-nitrogen cycle is possible ... 

A proposed series of reactions (known as the carbon-nitrogen cycle) that could be important in the very hottest region of the interior of the sun is... 

The sun with a central temperature of 15.7 million degrees, (Tg0 = 15.7) burns by p-p chains. Slightly more massive star (with central temperature Tq > 20) burns H by the CNO cycle also. Davis et al.s solar neutrino experiment [23], which in 1968 had only an upper limit of the neutrino flux, itself put a limit of less than 9% of the sun s energy is produced by the carbon-nitrogen cycle (the more recent upper limit [36] is 7.3%, from an analysis of several solar neutrino experiments, including the Kamland measurements). Note however that for the standard solar model, the actual contribution of CNO cycle to solar luminosity is 1.5% [15]). In CNO cycle, nuclei such as C, N, O serve as catalysts do in a chemical reaction. The pp-chain and the CNO cycle reaction sequences are illustrated in Figs. 4 and 10. 

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