We present ion-by-ion cooling efficiencies for low-density gas. We use Cloudy (version 10.00) to estimate the cooling efficiencies for each ion of the first 30 elements (H-Zn) individually. We present results for gas temperatures between 104 and 108 K, assuming low densities and optically thin conditions. When nonequilibrium ionization plays a significant role the ionization states deviate from those that obtain in collisional ionization equilibrium (CIE), and the local cooling efficiency at any given temperature depends on specific nonequilibrium ion fractions. The results presented here allow for an efficient estimate of the total cooling efficiency for any ionic composition. We also list the elemental cooling efficiencies assuming CIE conditions. These can be used to construct CIE cooling efficiencies for non-solar abundance ratios or to estimate the cooling due to elements not included in any nonequilibrium computation. All the computational results are listed in convenient online tables.

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Published in The Astrophysical Journal Supplement Series, v. 199, no. 1, 20, p. 1-5.

© 2012. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

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

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O.G. was supported by NASA through Chandra Postdoctoral Fellowship grant PF8-90053 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. Partial financial support for G.J.F's work on this project was provided by National Science Foundation grants AST 0908877 and AST 0607028, National Aeronautics and Space Administration grant 07-ATFP07-0124, and HST Theory grant AR 12125.01.

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Supplemental Data File: Table 1