HeII Case A Recombination Coefficients

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Alpha A HeII.png

The case A recombination coefficients for the HeII -> HeI transition. BS60 is my fit to the two data points in BS60. Black81 is another fit to the BS60 data that was subsequently used by Cen92 which was used by AAZN97. VF96 has the largest valid range, claiming an error of < 3% for T = 3 K to 106K. AP73 is calculated using the photoionisation data of Brown71 and claims to be accurate over T = 100 K to 105 K. It is used in Sherman79. HS98 is tabular data from T = 10 K to 25000 K.

Contents

BS60

Burgess & Seaton 1960 MNRAS 121, 471

T T1 / 2αA
1\times 10^4 43.1\times 10^{-18} \mathrm{m}^3 \mathrm{s}^{-1}
2\times 10^4 38.0\times 10^{-18} \mathrm{m}^3 \mathrm{s}^{-1}

My fit to BS60

\alpha^A_{HeII} = 2.30\times 10^{-16} \mathrm{m}^3 \mathrm{s}^{-1} T^{-0.6817}

Black81

Black 1981 MNRAS 197, 553

Fit to BS60 data:

\alpha^A_{HeII} = 1.50\times 10^{-16} \mathrm{m}^3 \mathrm{s}^{-1} T^{-0.6353}

T > 5000K

VF96

Verner & Ferland 1996, ApJS 103, 467

\alpha^A_{HeII} = a \left[ (T/T_0)^{1/2} (1+(T/T_0)^{1/2})^{1-b} (1+(T/T_1)^{1/2})^{1+b}\right]^{-1}

a=3.294\times 10^{-17}\mathrm{m}^3 \mathrm{s}^{-1}
b = 0.6910
T0 = 15.54K
T_1=3.676\times 10^7 \mathrm{K}

AP73

Aldrovandi & Pequignot 1973 A&A 25, 137

Used by Sherman79: Sherman 1979 ApJ 232, 1

\alpha^A_{HeII} = 2.10\times 16^{-16} \mathrm{m}^3 \mathrm{s}^{-1} T^{-0.672}

100 K < T < 10000 K

ET: Fit to HS98

\alpha_\mathrm{A HeII} = 1.27\times 10^{-16} T^{-0.5526} e^{-0.006875 \ln(T)^2}

HS98

Hummer & Storey 1998, MNRAS 297, 1073

log(T) α1[10 − 17m3s − 1] αB[10 − 17m3s − 1 ]
1.0 1.569 9.284
1.2 1.569 8.847
1.4 1.569 8.403
1.6 1.569 7.952
1.8 1.569 7.499
2.0 1.569 7.044
2.2 1.569 6.589
2.4 1.569 6.136
2.6 1.570 5.685
2.8 1.571 5.238
3.0 1.572 4.797
3.2 1.573 4.364
3.4 1.576 3.940
3.6 1.580 3.528
3.8 1.586 3.132
4.0 1.595 2.755
4.2 1.608 2.401
4.4 1.626 2.073

αA = α1 + αB

See Also

Recombination Coefficients

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