Adding Ionization and Recombination to CHIANTI

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					Adding Ionization and Recombination to CHIANTI

The CHIANTI database

Dr Peter Young CCLRC/Rutherford Appleton Laboratory, UK Dr Ken Dere George Mason University, USA

Background
• Tables of ion fractions as a function of temperature are essential for the analysis of electron-ionized plasmas • In the past, rates have been re-assessed on timescales of ~5 years and new tables published • Previous calculations include
– – – – Mazzotta et al. (1998) Arnaud & Raymond (1992) Arnaud & Rothenflug (1985) Shull & Van Steenberg (1982)

The CHIANTI database

CHIANTI
• CHIANTI contains atomic data for the calculation of level populations within ions • Major updates occur every ≈ 2 years
• There is no official CHIANTI ion fraction data-set • The user can choose any of the standard ion fraction tables

The CHIANTI database

CHIANTI version 6
• v.6 of CHIANTI will provide
– ionization rates – recombination rates – ion fractions derived from these rates

The CHIANTI database

Ionization
• Ionization rates have been assessed, and new calculations performed for many ions
– K.P. Dere (2006, submitted to ApJ)

• Experimental cross-section data have been fit with a Burgess & Tully (1992) type fitting formula

The CHIANTI database

f – scaling parameter; I – ionization potential; u = E/I; σ – cross-section

• High energy limit given by the Bethe coefficient

The CHIANTI database

Fitting the rates
• The ionization rate coefficients are also fit with a Burgess-Tully type scaling

f – scaling parameter; I – ionization potential; t = kT/I; σ – rate coefficient

The CHIANTI database

• The spline fits to these scaled rates will be provided to the CHIANTI user

Ionization: FAC calculations
• For many ions where experimental data are incomplete or missing, new data have been calculated
• The Flexible Atomic Code (FAC) has been used
– relativistic distorted wave code similar to that of Zhang & Sampson (1991)

The CHIANTI database

Example: Ni XIV

Radiative Recombination
• The baseline set of radiative recombination rates are derived from fits embedded in a fortran routine of D.A. Verner • Gives rates for all ions of all elements up to zinc
• These rates are used as the baseline, supplemented by
– Badnell (2006) – Wane & Aymar (1987) – Aldrovandi & Pequignot (1974)

The CHIANTI database

The CHIANTI database

Radiative Recombination Problems
• Beyond the sodium sequence, most of the data have been obtained by interpolation/extrapolation of the Woods et al. (1981) data-set for the iron ions • Comparisons with other data-sets show differences

The CHIANTI database

Dielectronic recombination
• Baseline DR rates are taken from Mazzotta et al. (1998)
• New DR rates for all sequences up to the sodium sequence have been calculated by N.R. Badnell and co-workers

• Rates for Cu and Zn were not provided by Mazzotta et al. (1998). These are taken from Mazzitelli & Mattioli (ADNDT, 2002)

The CHIANTI database

The CHIANTI database

Comparison with Nahar data
• S. Nahar and colleagues have calculated combined RR and DR rates for many ions
• Significant differences exist for some ions for cases where new Badnell data are available, and also where older data are being used

The CHIANTI database

Blue curve: Badnell data

Red curve: Nahar data

The CHIANTI database

Blue curve: Mazzotta data

Red curve: Nahar data

The CHIANTI database

New CHIANTI ion balance
• Carbon ions

The CHIANTI database

Conclusions
• Version 6 of CHIANTI should be ready in around 6 months
• For all ions of all elements up to zinc it will contain
– ionization rates – recombination rates – ion fraction curves

The CHIANTI database


				
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