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

Comments

This data is also in Chianti , although in a different form. So we could potentially use this data as part of a push to just use Chianti for all our data uses. An updated set of DI data is available here