Known Problems with C08

This page lists the known problems with this version of Cloudy. A known problem means that we know about the problem but the fix is too difficult to implement in the current version.

Format for known problems: We should include a simple description of the problem itself, avoiding computer or physics jargon, an estimate of when and how the problem will be fixed, an acknowledgment to the person who pointed out the problem if appropriate, and the date when the problem was entered on this page.


C08.00

There are minor problems with the low-T dielectronic recombination rates

Hazy claims that averaged low-T dielectronic recombination rates (maily from Badnell) will be used for all ions for which no reliable data exist. This was our intention, but is not how things are implemented in C08. The Ali et al. (1991) assumed rates are still being used by default if the ion recombines to one of the lowest four ionization stages of an element and no better data exist. The Ali et al. (1991) rates will be completely removed in the next release. The Kraemer et al. DR rates are never used, no matter what input options are given.

The set dielectronic recombination kludge noise command requires the kludge keyword to be present. This has been omitted in Hazy. This command is currently broken, but as a temporary work-around the keyword badnell can be added. This avoids the problem. All of this will be fixed in the next release as well.

2008 Sep 23

Energy is not conserved in vastly optically thick environments.

The total radiated power is less than the input luminosity when AV is 100 or larger. This will be fixed in the next major release. Thanks to Nick Abel and Norm Murray for pointing this out.

2007 Nov 26

Molecular opacities in dust-free environments

Most molecular environments are also dusty. This assumption is behind nearly all ISM chemistry codes (see the comparison given in Roellig et al. 2007, available  here). Cloudy includes a complete treatment of x-ray opacities for all elements in grains and molecules, and a detailed treatment of opacity for grains, H-, H2, and CO. But the code follows the UMIST approach for minor molecules. This includes writing many molecular photo rates as a function of the incident radiation field and the total dust extinction. The opacity contributed by minor molecules is ignored.

The innermost regions of dense circumstellar disks may be molecular and, if hot enough, dust free. Species such as TiO may become important opacity sources. Their opacities are not now included. The code is not now applicable to this environment.

This is on our to-do list but the technical problems are vast. The chemistry of TiO in the ISM has not been worked out in detail since Ti is very highly depleted. Stellar atmosphere-based codes do TiO chemistry assuming thermodynamic relationships which do not apply to low-density environments. For now, the code is not applicable to dust-free molecular clouds when minor molecules are important opacity sources.

Many thanks to Andrea Isella for pointing out this problem.

2007 June 15


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