Collisional Ionization Equilibrium for Optically Thin Plasmas. I. Updated Recombination Rate Coefficients for Bare through Sodium‐like Ions

Abstract

Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and are often highly suspect. This translates directly into the reliability of the collisional ionization equilibrium (CIE) calculations. We make use of state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He up to and including Zn. Where measurements exist, these published theoretical DR data agree with recent laboratory work to within typically 35% or better at the temperatures relevant for CIE. We also make use of state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H through to Zn. Here we present improved CIE calculations for temperatures from 10 4 to 10 9 K using our data and the recommended electron impact ionization data of Mazzotta et al. for elements up to and including Ni and Mazzotta for Cu and Zn. DR and RR data for ionization stages that have not been updated are also taken from these two additional sources. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. for all elements from H to Ni. The differences in peak fractional abundance are up to 60%. We also compare with the fractional ionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR calculations of Gu for the H-like through Na-like ions, and the RR calculations of Gu for the bare through F-like ions. These results are in better agreement with our work, with differences in peak fractional abundance of less than 10%.

Experimental rate coefficients of F5+recombining into F4+

“…They have found that for some ions the uncertainties in different calculations can be as large as a factor of 2−5. More recently, Bryans et al (2006) used updates to archived DR and RR data to find differences in peak fractional abundances of up to 60% compared to the commonly used data. Because of these uncertainties in low-temperature plasma rates, the relative elemental abundance inferred from the solar and stellar upper atmosphere, needed for modelling the astrophysical plasmas is A&A 557, A2 (2013) affected to a large extent (Chen 2002).…”

Experimental dielectronic recombination rate coefficients for Na-like S VI and Na-like Ar VIII

“…DR is a strong recombination channel at plasma temperatures where highly charged ions are common. In the calculation of fractional abundances of various charge states the results depend crucially on the atomic data used as input in the calculations (Bryans et al 2006). Sulfur and argon are astrophysically abundant elements (Anders & Grevesse 1989), accurate DR rate coefficients for their ions are thus important for the diagnostics and modeling of astrophysical plasmas.…”

“…Generally, for open L and M shell ions the discrepancies between the results of state-of-the-art calculations amount to ∼35% (Bryans et al 2006). For DR resonances below 1−3 eV energy, the uncertainties are much higher, due to the inability of modern theory to accurately predict resonance positions, widths and strengths.…”

The ionization balance of a non-equilibrium plasma

“…strath.ac.uk/tamoc/DR/. The total DR recombination rate is now substantially higher at temperatures below the ionization peak with the result that the gas tends to be more neutral (Bryans et al 2006(Bryans et al , 2009.…”