We present improved fits to our treatment of suppression of dielectronic recombination at intermediate densities. At low densities, most recombined excited states eventually decay to the ground state, and therefore the total dielectronic recombination rate to all levels is preserved. At intermediate densities, on the other hand, collisions can lead to ionization of higher-lying excited states, thereby suppressing the dielectronic recombination rate. The improved suppression factors presented here, although highly approximate, allow summed recombination rate coefficients to be used to intermediate densities. There have been several technical improvements to our previously presented fits. For H- through B-like ions the activation log densities have been adjusted to better reproduce existing data. For B-, C-, Al-, and Si-like ions secondary autoionization is now included. The treatment of density discontinuity in electron excitations out of ground state H-, He-, and Ne-like ions has been improved. These refined dielectronic recombination suppression factors are used in the most recent version of the plasma simulation code Cloudy. We show how the ionization and emission spectrum change when this physics is included. Although these suppression factors improve the treatment of intermediate densities, they are highly approximate and are not a substitution for a complete collisional-radiative model of the ionization balance.

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Published in The Astrophysical Journal Supplement Series, v. 237, no. 2, 41, p. 1-14.

© 2018. The American Astronomical Society. All rights reserved.

The copyright holder has granted the permission for posting the article here.

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Funding Information

T.W.G. was supported in part by NASA (NNX11AF32G and NNX17AD41G). K.T.K. was supported in part by NASA (NNX11AF32G). M.C. acknowledges support from NASA Program number HST-AR-14556.001-A through a grant from the Space Telescope Science Institute. G.J.F. acknowledges support by NSF (1108928; and 1109061), NASA (10-ATP10-0053, 10-ADAP10-0073, and NNX12AH73G), and STScI (HST-AR-12125.01, GO-12560, and HST-GO-12309). F.G. acknowledges support by NSF (1412155). P.v.H. was supported by the Belgian Federal Science Policy Office under contract No. BR/143/A2/BRASS. N.R.B. acknowledges support by STFC (ST/J000892/1).

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