Peter Young* George Mason University, VA Uri Feldman Artep Inc, MD *Work funded by NSF and NASA

Atomic data and software package for modeling emission lines – ions and neutrals for elements up to zinc – software written in IDL and Python First released in 1996 (Dere et al. 1997, A&AS) Latest version: 7.1 (Landi et al. 2013, ApJ) Citations: 1943 Large effort gone into benchmarking atomic data against observations CHIANTI atomic data are used in other codes (CLOUDY, APED, MOCASSIN, XSTAR) Dr Peter Young (GMU) Team members Ken Dere Giulio Del Zanna Enrico Landi Helen Mason Peter Young

CHIANTI contains atomic data for solving level balance equations for atoms and ions Principal data-sets are: – electron excitation rates – radiative decay rates – experimental energy levels Dr Peter Young (GMU)

Level balance equations are α ji are atomic rate coefficients (radiative decay rates, electron excitation rates, etc.) n j are the level populations (normalized so that Σ n j = 1) Dr Peter Young (GMU) n j computed with CHIANTI IDL routines pop_solver.pro & show_pops.pro Method is to plot the n j along an isoelectronic sequence -Set temperature to be T max of ion -Use density cm -3

Example of a ‘good’ case Dr Peter Young (GMU)

An atomic data error clearly seen for N VI Dr Peter Young (GMU) 2-photon transition had been incorrectly assigned Fixed with recent v7.1.4 release

For 2p 3 levels an apparent anomaly for iron is seen Dr Peter Young (GMU)

The excited ground configuration levels of high-Z ions gain significant population only at high densities Consider 2s2p 3 3 P 0 (index=10) level of C-like ions Dr Peter Young (GMU) => High-Z ion models are much more sensitive to the accuracy of weak transitions Si IX (log T = 6.0)Fe XXI (log T = 7.1) Level nini q i,10 n i q i,10 nini q i,10 n i q i,10 3P03P (-12)6.9(-13)1.06.9(-13) 3P13P (-10)1.8(-10)9.2(-4)8.0(-11)7.4(-14) Weak 3 P 0 – 3 P 0 transition is dominant excitation channel Density=10 10 cm -3

Why is the population for Fe XXI 2s 2p 3 3 P 0 enhanced? Fe XXI has 621 levels; Mn XX has 20 levels Dr Peter Young (GMU) Mn XXFe XXI Contrib.LevelProcessContrib.LevelProcess 56.8%1e exc.49.2%1e exc. 42.8%2e exc.26.0%25cascade 4.9%2e exc. 3.9%26cascade The ground level excitation rate is much higher for Fe XXI

Big difference in collision strengths for weak ground level excitation Dr Peter Young (GMU) Mn XX: Zhang & Sampson (1996, ADNDT, 63, 275) – distorted wave Fe XXI: Badnell & Griffin (2001, J.Phys.B, 34, 681) – R-matrix Iron bump caused by 1.enhanced direct excitation rates 2.cascading from high levels

With CHIANTI 8 (coming soon!) we will distribute an IDL routine to plot isoelectronic level populations For investigating population processes of a specific level, use Dr Peter Young (GMU) IDL> ch_plot_iso_pops, ‘o_6’, 3 (plots isoelectronic populations for the level identified as no. 3 for O VI -> 1s 2 2p 2 P 3/2 ) IDL> pop_processes, ‘o_6’, lev=3, /verbose Into levelOut of level Radiative decay0.5 %100.0 % Electron excitation99.5 %0.0 % already in CHIANTI

Studying level populations along isoelectronic sequences is a good way of assessing atomic data accuracy. The method focuses attention on those atomic data that most influence the populations (and hence emissivities) of the ions. For Z ≥ 20 large atomic models are critical for modeling weak ground-level excitations. Software will be distributed with CHIANTI 8. Dr Peter Young (GMU) See online talk for He- to Na-like sequences (

Minor elements show large differences (e.g., P X vs. S XI) Dr Peter Young (GMU)

Factor 10 difference in level population for 2p 4 1 S 0 level – why? Error for P X oscillator strength Dr Peter Young (GMU) TransitionZhang & Sampson (1996)CHIANTI 2s 2p 3 1 P 1 - 2p 4 1 S The Z&S data have been replaced for the abundant elements, but not the minor elements

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