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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 network, aprox13.tbz, uses 13 isotopes in an alpha-chain from helium to nickel. Helium burning and heavy-ion (12C+12C, 12C+16O, 16O+16O) are included. A definition of what I mean by an α-chain reaction network is prudent. A 'strict' α-chain reaction network 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. In this α-chain reaction network, I include 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. Thus, this α-chain reaction network includes not just (α,γ) and (γ,α) links, but also links through the (α,p)(p,γ) and (γ,p)(p,α) sequences.

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13 isotope jacobian
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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 (ApJ 225, 1021, 1978).

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strong c+o burn
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19 isotope jacobian

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

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

7 isotopes
To decrease the computer 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.In essence, one gets most of the energy generated for most thermodynamic conditions at a fraction of the computational cost (memory + CPU). 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, is described in "An Inexpensive Nuclear Energy Generation Network For Stellar Hydrodynamics". This network is shown to give a good representation of nuclear energy generation rates during helium, carbon, neon, and oxygen burning. It even gives reasonable estimates for the energy generation rates during silicon burning and photodisintegration reactions. This network may be useful for exploratory multi-dimensional calculations where large reaction networks are impractical even on the largest parallel supercomputers.
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7 vs 13 isotopes
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7 vs 490 isotopes

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

 



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