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Alpha-chain reaction networks

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Contact: F.X.Timmes
my one page vitae,
full vitae,
research statement, and
teaching statement.

13 isotopes
This reaction network, aprox13.tbz, uses 13 isotopes in an alpha-chain from helium to nickel. Heavy-ion (12C+12C, 12C+16O, 16O+16O) are included. A definition of an α-chain reaction network seems prudent. A 'strict' α-chain is only composed of (α,γ) and (γ,α) links among the 13 isotopes 4He, 12C, 16O, 20Ne, 24Mg, 28Si, 32S, 36Ar, 40Ca, 44Ti, 48Cr, 52Fe, and 56Ni. It is essential, however, to include (α,p)(p,γ) and (γ,p)(p,α) links in order to obtain reasonably accurate energy generation rates and abundance levels when the temperature exceeds 2.5e9 K. At these elevated temperatures the flows through the (α,p)(p,γ) sequences are faster than the flows through the (α,γ) channels. An (α,p)(p,γ) sequence is, effectively, an (α,γ) reaction through an intermediate isotope. This α-chain reaction network includes 8 (α,p)(p,γ) sequences plus the corresponding inverse sequences by assuming steady-state proton flows through the intermediate isotopes 27Al, 31P, 35Cl, 39K, 43Sc, 47V, 51Mn, and 55Co. This strategy permits inclusion of (α,p)(p,γ) sequences without explicitly evolving the proton or intermediate isotope abundances.

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image Jacobian matrix image A mild c+o burn

19 isotopes
This network, aprox19.tbz, is the same network as the 13 isotope network above with additional isotopes to accommodate some types of hydrogen burning (PP chains and steady-state CNO cycles), along with some aspects of photodisintegration into 54Fe. This network is described in Weaver, Zimmerman, & Woosley.

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image image A strong c+o burn

21 isotopes
This network, aprox21.tbz, adds 56Cr and 56Fe and equilibrium reaction sequences to the 19 isotope network to attain a lower Ye for presupernova models. This network is more-or-less the default workhorse network of MESA.


image

image Abundances and Ye evolution (and for the 19 isotope network)


34 isotopes
This reaction network, hhe.tbz, combines the pp + hotcno + rp breakout network with the 13 isotope network above for a complete hydrogen + helium burner under most common conditions.

7 isotopes
To decrease the execution time and memory it takes to calculate a stellar model means making a choice between having fewer isotopes in the reaction network or having less spatial resolution. The general response to this tradeoff has been to evolve a limited number of isotopes, and thus thus calculate an approximate thermonuclear energy generation rate. The 13 isotope network given above is commonly used for this purpose; one gets most of the energy generated for common thermodynamic conditions at a fraction of the computational cost. Can the number of isotopes be further reduced, and still give relatively accurate energy generation rates? Yes, within reason. This 7 isotope α-chain network, iso7.tbz, has been shown to provide a decent representation of nuclear energy generation rates for helium to silicon burning.
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