New in C84

This page summarizes all major changes and improvements to Cloudy that will be included in the next release. You may also view the HotFixes and KnownProblems pages, or return to the main RevisionHistory page.


In previous versions of the code both luminosity (quantity radiated into 4p sr) and intensity (a surface flux) were specified with the same command. The code decided which was intended by checking the resulting ionization parameter. This method never failed to the best of my knowledge, but, as the code grows more capable of considering ever more extreme cases, there might eventually come a time when it made the wrong decision. All luminosity-intensity commands have now been split up. For instance, the Q(H) command is now two commands, Q(H) (for number of photons radiated into 4p sr) and f(H), for the surface flux. These commands are all discussed in Part I of Hazy.

Mg II l2798

The biggest difference between the two versions is in the predicted intensity of Mg II l2798. The intensity of this line is now a factor of two stronger in many models. The new version uses L-shell photoabsorption cross sections from Reilman and Manson (1979), and the older version used inner shell cross sections extrapolated from the table in Weisheit (1974). The cross sections differ by a factor of nearly 3, in the sense that Mg now tends to be more neutral, and Mg II stronger. As a result of the increased cooling by l2798 other lines formed in the same region tend to be weaker.

General Results

The following may affect certain specific models, but did not result in changes in any of the “standard” test cases.

The treatment of line-continuum fluorescence in the optically thin limit has been much improved, following Ferland (1992). This can affect hydrogen line emission in clouds that are optically thin in the Lyman continuum.

The treatment of molecules has been vastly improved. The code now goes to the fully molecular (H2 and CO) limit, and reproduces the Tielens and Hollenbach (1985a, b) PDR results for Orion.

The elements Na and Ni have been added.

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Last modified 2 years ago Last modified on 2018-03-05T12:42:18Z