Direct Ionization
This is the data to compute ionization rates from collisions between ions and hot electrons.
Source
The data comes directly from Dere 2006, A&A, 466, 771 . This paper gives direct ionization and excitation-autoionization rate coefficients for many ions as a function of temperature for Maxwellian electron distributions.
Translation to Python format
The data table is downloaded in its entirety from the data table associated with the paper. All that happens is that the table is saved to a text file, and the keyword DI_DERE is just prepended to each row.
Data format
Each line starts with the label DI_DERE and then follows
Nuclear Charge - z - used to identify the ion
Ion - state in our normal notation, so 1=neutral
Number of splines N- the number of spline points for the fit of rate coefficients vs scaled temperature
Scaled temperatures - there are N of these
Scaled Rate coefficients - N of these
The scaled temperatures are given by
\(x=1-\frac{\log{f}}{\log(t+f)}\)
where t=kT/I. I is the ionization potential, and f=2.0. The rate coefficient R(T) is recovered from the scaled rate coefficient in the table, $rho$ using
\(\rho=t^{1/2}I^{3/2}R(T)/E_{1}(1/t)\)
where \(E\_{1}\) is the first exponential integral. In python we use the gsl_sf_expint_E1 routine in gsl.
Python structure
This data is stored in the dere_di_rate structure with members
int nion- Internal cross reference to the ion that this refers to
int nspline - the number of spline points that the fit is evaluated over
double temps[DERE_DI_PARAMS]- temperatures at which the rate is tabulated
double rates[DERE_DI_PARAMS]- rates corresponding to those temperatures
double xi - the ionization energy of this ion
double min_temp -the minimum temperature to which this rate should be applied