We examine a number of molecular ratios which could be used as indicators of such an impending changeover. The changeover in spectral appearance should be quite quick as the star evolves from type M to type C. Four of the cases would be able to evolve into carbon stars if the mixing were extensive enough. The possible atomic and molecular abundaces for each case were calculated as a function of the amount of mixing between envelope and interior material. Seven cases were studied, the difference between them being the length of time, during which the interior material had been exposed to the CNO-process.
International Nuclear Information System (INIS)Ĭompositions of red giant atmospheres have been calculated assuming an envelope in which solar abundances have been mixed with CNO-processed material from the interior. The role of the CNO-cycle in M- and C-stars Finally, the impact of the experimental and theoretical results on our present understanding of hydrogen burning in different stellar environments is presented, as well as the impact on our understanding of the chemical evolution of our universe. This development emerged from the detailed experimental studies of the associated nuclear reactions over more than seven decades. Further, the experimental verification of the predicted process as it developed over the following decades is discussed, as well as the extension of the initial carbon cycle to the carbon-nitrogen-oxygen ( CNO) multi- cycles and the hot CNO cycles. In particular, it addresses the contributions of Carl Friedrich von Weizsäcker and Hans Bethe, who provided the first predictions of the carbon cycle. This paper presents the intellectual and historical background of the idea of the correlation between stellar energy production and the synthesis of the chemical elements in stars on the example of this cycle. The carbon cycle, or Bethe-Weizsäcker cycle, plays an important role in astrophysics as one of the most important energy sources for quiescent and explosive hydrogen burning in stars. The History and Impact of the CNO Cycles in Nuclear Astrophysics
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