[mesa-users] approx13
Ken Shen
kenshen at astro.berkeley.edu
Wed May 14 17:09:06 EDT 2014
Hi all. I've been trying to construct a nuclear network in MESA that
mimics Frank Timmes's approx13, which is an alpha-network that contains
4He, 12C, 16O, 20Ne, etc. up to 56Ni. It contains the 12x2 (a,g) and (g,a)
forward and reverse reactions linking each adjacent isotope (e.g.,
12C(a,g)16O); 3 heavy-ion forward reactions (12C+12C, 12C+16O, 16O+16O);
and 8x4 (a,p)(p,g) forward and reverse p-catalyzed alpha-captures starting
at 24Mg(a,p)(p,g)28Si. These hardwired reactions assume the intermediate
isotopes (e.g., 27Al) are in equilibrium with the reactions that involve
them.
MESA (version 5596) gives me an error when I don't include protons in the
network (why is that?), so I've added them in, but no reactions link
directly to them, so their mass fraction should stay zero (and does). I've
attached the naive .net file I came up with, based off approx_base.net, at
the bottom of the email.
The problem is that this network doesn't give the correct burning results.
At T = 3e9 K and rho = 1e7 g/cm^3, a pure 12C composition results in
epsilon = 1.8e19 erg/(g*s), which is about 4 orders of magnitude too low.
I eventually stumbled across a fix, which is to include neutrons in the
isotope list. As with protons, neutrons don't show up explicitly in the
network and their mass fraction stays constant at zero, but the burning
goes up to the correct value.
Furthermore, with neutrons and protons included in the isotopes list, a
pure 16O composition at the same T and rho yields epsilon = 6.3e17. Adding
1H to the list (again, not part of the actual network) yields epsilon =
7.3e17.
Any enlightenment out there?
! Naive approx13.net file
add_isos(
prot
he4
c12
o16
ne20
mg24
si28
s32
ar36
ca40
ti44
cr48
fe52
ni56
)
add_reactions(
! triple alpha
r_he4_he4_he4_to_c12
r_c12_to_he4_he4_he4
! C/O burning
r1212 ! c12 + c12 -> ne20 + he4, includes na23+p
channel
r1216_to_mg24 ! c12 + o16 -> mg24 + he4
r1216_to_si28 ! c12 + o16 -> si28
r1616a ! o16(o16a)si28
r1616ppa ! o16(o16p)p31(pa)si28
r1616ppg ! o16(o16p)p31(pg)s32
r1616g ! o16(o16g)s32
r1616p_aux ! o16(o16p)p31
! alpha links with both (a,g) and (a,p)(p,g)
! o16
! from c12 by (a,g)
r_c12_ag_o16
r_o16_ga_c12
! ne20
! from o16 by (a,g)
r_o16_ag_ne20
r_ne20_ga_o16
! mg24
! from ne20 by (a,g)
r_ne20_ag_mg24
r_mg24_ga_ne20
! si28
! from mg24 by (a,g)
r_mg24_ag_si28
r_si28_ga_mg24
! from mg24 by (a,p)(p,g) via al27
rmg24ap_to_si28 ! mg24(ap)al27(pg)si28
rsi28gp_to_mg24 ! si28(gp)al27(pa)mg24
rmg24ap_aux ! mg24(ap)al27
ral27pg_aux ! al27(pg)si28
rsi28gp_aux ! si28(gp)al27
ral27pa_aux ! al27(pa)mg24
! s32
! from si28 by (a,g)
r_si28_ag_s32
r_s32_ga_si28
! from si28 by (a,p)(p,g) via p31
rsi28ap_to_s32 ! si28(ap)p31(pg)s32
rs32gp_to_si28 ! s32(gp)p31(pa)si28
rsi28ap_aux ! si28(ap)p31
rp31pg_aux ! p31(pg)s32
rs32gp_aux ! s32(gp)p31
rp31pa_aux ! p31(pa)si28
! ar36
! from s32 by (a,g)
r_s32_ag_ar36
r_ar36_ga_s32
! from s32 by (a,p)(p,g) via cl35
rs32ap_to_ar36 ! s32(ap)cl35(pg)ar36
rar36gp_to_s32 ! ar36(gp)cl35(pa)s32
rs32ap_aux ! s32(ap)cl35
rcl35pg_aux ! cl35(pg)ar36
rar36gp_aux ! ar36(gp)cl35
rcl35pa_aux ! cl35(pa)s32
! ca40
! from ar36 by (a,g)
r_ar36_ag_ca40
r_ca40_ga_ar36
! from ar36 by (a,p)(p,g) via k39
rar36ap_to_ca40 ! ar36(ap)k39(pg)ca40
rca40gp_to_ar36 ! ca40(gp)k39(pa)ar36
rar36ap_aux ! ar36(ap)k39
rk39pg_aux ! k39(pg)ca40
rca40gp_aux ! ca40(gp)k39
rk39pa_aux ! k39(pa)ar36
! ti44
! from ca40 by (a,g)
r_ca40_ag_ti44
r_ti44_ga_ca40
! from ca40 by (a,p)(p,g) via sc43
rca40ap_to_ti44 ! ca40(ap)sc43(pg)ti44
rti44gp_to_ca40 ! ti44(gp)sc43(pa)ca40
rca40ap_aux ! ca40(ap)sc43
rsc43pg_aux ! sc43(pg)ti44
rti44gp_aux ! ti44(gp)sc43
rsc43pa_aux ! sc43(pa)ca40
! cr48
! from ti44 by (a,g)
r_ti44_ag_cr48
r_cr48_ga_ti44
! from ti44 by (a,p)(p,g) via v47
rti44ap_to_cr48 ! ti44(ap)v47(pg)cr48
rcr48gp_to_ti44 ! cr48(gp)v47(pa)ti44
rti44ap_aux ! ti44(ap)v47
rv47pg_aux ! v47(pg)cr48
rcr48gp_aux ! cr48(gp)v47
rv47pa_aux ! v47(pa)ti44
! fe52
! from cr48 by (a,g)
r_cr48_ag_fe52
r_fe52_ga_cr48
! from cr48 by (a,p)(p,g) via mn51
rcr48ap_to_fe52 ! cr48(ap)mn51(pg)fe52
rfe52gp_to_cr48 ! fe52(gp)mn51(pa)cr48
rcr48ap_aux ! cr48(ap)mn51
rmn51pg_aux ! mn51(pg)fe52
rfe52gp_aux ! fe52(gp)mn51
rmn51pa_aux ! mn51(pa)cr48
! ni56
! from fe52 by (a,g)
r_fe52_ag_ni56
r_ni56_ga_fe52
! from fe52 by (a,p)(p,g) via co55
rfe52ap_to_ni56 ! fe52(ap)co55(pg)ni56
rni56gp_to_fe52 ! ni56(gp)co55(pa)fe52
rfe52ap_aux ! fe52(ap)co55
rco55pg_aux ! co55(pg)ni56
rni56gp_aux ! ni56(gp)co55
rco55pa_aux ! co55(pa)fe52
)
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