Stellar Nucleosynthesis

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The main branch1 12 C + p → 13 N + γ2 13 N → 13 C + e + + ν e3 13 C + p → 14 N + γ4 14 N + p → 15 O + γ5 15 O → 15 N + e + + ν e6 15 N + p → 12 C + 4 HeIn the steady state case, the abundancesof isotopes must take values such that theisotopes which react more slowly havehigher abundance. The slowest reaction isp capture by 14 N . Hence most of 12 C isconverted to 14 N.20Slide: Stephen Smartt
Temperature dependence of PP chain andCNO CycleThe two processes have very different temperature dependences. The rate of energyproduction in each:ε PP= ε 0ρX H2⎛⎛⎜⎜⎝⎝TT 0⎞⎞⎟⎟⎠⎠4.6⎛⎛ T ⎞⎞ε CNO= ε 0ρX HX CNOf N ⎜⎜ ⎟⎟⎝⎝ 25 ×10 6 ⎠⎠16.7€Equating this two gives the T at which they produce the same rate of energyproduction:€ ⎛⎛ XT ≈1.7 ×10 7 H⎞⎞⎜⎜ ⎟⎟⎝⎝ 50X CN ⎠⎠112.1KBelow this temperature the PP chain is most important, and above it the CNO Cycledominates. This occurs in stars slightly more massive than the sun e.g. 1.2-1.5M .€21Slide: Stephen Smartt
Page 1 and 2: Stellar NucleosynthesisThey Might b
Page 3 and 4: Abundances of nuclei3Slide: Stephen
Page 5 and 6: Review: Binding Energy of Nuclei
Page 7 and 8: Rate of Reactions
Page 9 and 10: Occurrence of fusion reactionsNow w
Page 11 and 12: The Gamow peakSchematically this is
Page 13 and 14: ResonancesResonanceC 12 + P => N 13
Page 15 and 16: Relative importance of PPIand PPII
Page 17 and 18: When does a given P-P chain dominat
Page 19: The CNO CycleAt birth stars contain
Page 23 and 24: Changes in Elemental Abundances Dur
Page 25 and 26: Helium Burning: the triple-α react
Page 27 and 28: Carbon and oxygen burningCarbon bur
Page 29 and 30: Major nuclear burning processesComm
Page 31 and 32: In the process two types of reactio
Page 33: 1.We described the basic accounting

Stellar Nucleosynthesis

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