Opened 8 months ago

Last modified 8 months ago

#404 new enhancement


Reported by: peter Owned by: nobody
Priority: good to do Milestone: C19_branch
Component: atomic/molecular data base Version:
Keywords: Cc:


A frequently asked question is: what is the critical density for collisional de-excitation of level xxx in some atom or ion. The answer changes every time the atomic data is updated. So it would be useful to have a print command that gives this information based on the atomic data that is in Cloudy. The syntax could be something like

PRINT CRITICAL DENSITY <species> [ levels = n ] [ Te = T ]

which would print the critical density for the lowest n levels (excluding the ground level of course). The default for n could be 5 and the default for Te could be 10,000 K.

Change History (3)

comment:1 Changed 8 months ago by peter

Gary replied:

We already have that in the SAVE LINE DATA ouput. Here is a sample of the output:

Level 2 transferred lines

#Ion WL gl gu gf A CS n(crt) damp

the critical density is the n(crt) number. It is evaluated at save_linedata.cpp:335 using the stored collision strength.

but this was not consistently supported as the lines were developed. we need to check that Coll().col_str() is really kept up to date for electrons, And make it clear that this is an electron collision strength. there are species in PDRs where atomic collisions may be more important.

comment:2 Changed 8 months ago by peter

Peter replied:

I searched Hazy 1 for the string "critical density" before opening this ticket. It popped up nothing relevant. This feature in the SAVE LINE DATA output is not documented.

I also see other problems. We always say that the critical density is a feature of a level and not a line, so it is confusing to have it as part of the SAVE LINE DATA output.

A quick look suggests to me that the formula used to calculate the critical density does not agree with Eq. 3.30 in AGN3.

comment:3 Changed 8 months ago by peter

Gary replied:

OK - I agree. it should be defined in the level solver, just after the matrix is set up. the info is all there.

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