CHIANTI -- an atomic database for emission lines -- Paper XVIII. Version 11, advanced ionization equilibrium models: density and charge transfer effects

TL;DR

The paper presents Version 11 of the CHIANTI atomic database, introducing advanced ionization equilibrium models that account for density and charge transfer effects, significantly improving the accuracy of emission line predictions in the solar transition region.

Contribution

It introduces new ionization models for low charge states that incorporate density and charge transfer effects, enhancing modeling accuracy for high-density plasma environments.

Findings

Predicted line radiances increased by factors of 2-5 for key UV lines.

Achieved within 20% agreement with observed spectra.

Improved modeling of the solar transition region.

Abstract

Version 11 of the CHIANTI database and software package is presented. Advanced ionization equilibrium models have been added for low charge states of seven elements (C, N, O, Ne, Mg, Si and S), and represent a significant improvement especially when modelling the solar transition region. The models include the effects of higher electron density and charge transfer on ionization and recombination rates. As an illustration of the difference these models make, a synthetic spectrum is calculated for an electron pressure of 7$\times 10^{15}$ cm$^{-3}$ K and compared with an active region observation from HRTS. Increases are seen of factors of two to five in the predicted radiances of the strongest lines in the UV from Si IV, C IV, and N V, compared to the previous modelling using the coronal approximation. Much better agreement (within 20\%) with the observation is found for the majority of the lines. The new atomic models better equip both those who are studying the transition region and those who are interpreting emission from higher density astrophysical and laboratory plasma. In addition to the advanced models, several ion datasets have been added or updated, and data for the radiative recombination energy loss rate have been updated.