CNO cycle All initial abundances within a cycle serve as catalysts and accumulate at largest  Extended cycles introduce outside material into CN cycle (Oxygen, … Energetics: Q = Q 4p  4He – E = MeV – MeV – MeV = MeV 13 N(  +) 15 O(  +) neutron number C(6) N(7) O(8) F(9) Ne(10) CN cycle (99.9%)O Extension 1 (0.1%) O Extension 2 O Extension 3

Cold CNO cycle Hot CNO cycle

CNO cycle abundance evolution into steady state (from Iliadis)

Competition between the p-p chain and the CNO Cycle The main reason are different slopes due to different temperature dependencies of p+p and 14N(p,g)

Competition between the p-p chain and the CNO Cycle But exact cross over also depends on other variables: So in addition to the reaction rates the ratio depends on initial CN abundance Y CNinitial current H abundance Yp different neutrino loss fractions So in addition to the reaction rates the ratio depends on initial CN abundance Y CNinitial current H abundance Yp different neutrino loss fractions