Known Problems with C10

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.


C10.00

Updating the grain opacities

Cloudy version C10.00 and all previous releases since 2004 contain a bug causing the overall sum of the grain opacities not to be updated as often as necessary. This bug will affect all models containing grains with variable abundances, most notably PAHs. The effect of the bug is not easily predictable and can only be reliably checked by rerunning the sims in question with a patched version of the code. Rerunning our test suites shows that typical PDR lines such as [C I], [C II], [O I] and the CO lines are affected, most notably in sims that include both the H+ region and the PDR. The most important effect is that the gas temperature in the PDR is off due to an incorrect amount of grain-gas collisional energy exchange.

To fix this bug you need to edit the file grains.cpp and change line number 4098 from

if( rfield.nflux > gv.nfill || ( gv.lgAnyDustVary && nzone != gv.nzone ) || lgChangeCS_PDT ) // wrong

to

if( rfield.nflux > gv.nfill || gv.lgAnyDustVary || lgChangeCS_PDT ) // correct

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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