Basic Information on lvg

Task: lvg
Purpose: Calculates LVG radiative transfer models.
Categories: models

LVG calculates a 1-D, 2-D, or 3-D grid of lvg radiative transfer
models as specified by the input parameters. When a range of
values is specified for a parameter (density, temperature, fractional
abundance, column density), models are logrithmically spaced over the
interval.

Key: mol
Name of molecule. Known molecules are CO, CS, etc. No Default.

Key: iso
Isotope of molecule if other than main isotopic species. Default
is main isotopic species.

Key: den
Density range to be covered by the model grid. Input may be one, two,
or three numbers. The first number indicates the number of density
models to be calculated; the second and third numbers specify the density 
of the first and last models in particles/cm3. Models are logrithmically 
spaced. If only two numbers are given, the density for all models is set 
to the second number. If only one number is given, the default density 
is assumed. 
Example: den = 5,1.0e4,1.0e6 -- 5 models with densities from 1.0e4 to 1.0e6.
Defaults = 1,10000.

Key: xmol
Range of fractional abundance of molecule to be used in calculation. 
Input may be one, two, or three numbers as above. 
WARNING -- xmol and cd can not be non-zero simultaneously. 
Default = 0,1.0e-8

Key: cd
Range in molecular column density to be used in calculation. Input
may be one, two, or three numbers; see description of density for more 
format information. 
WARNING -- xmol and cd can not be non-zero simultaneously. 
Default = 1,1.0e12.

Key: tk
Range of kinetic temperature to be used in calculating models. Input
may be one, two, or three numbers; see description of density for more 
format information. 
Default = 1,20

Key: dv
Velocity FWHM of line in km/sec. CD will be divided by this value
for calculating the radiative excitation.

Key: iter
Maximum number of iterations allowed for each model. Usually the defaults 
is fine but models with high opacity and low density may require more 
iterations.
Default = 25.

Key: tbkg
Blackbody temperature for background radiation field in all transitions. 
Normally set to the cosmic background temperature.
Default = 2.78.

Key: pops
Data file name for level populations. 
Two or three of den, xmol, cd, or tk must be specified with more than
1 model along that axis. If no name is given, no file will be written. 
Default: '  '

Key: trads
Data file name for line radiation temperatures.
Two of den, xmol, cd, or tk must be specified with more than
1 model along that axis. If no name is given, no file will be written. 
Default: '  '

Key: trans
List of frequencies (in GHz) of transitions to be included in 'trads' file. 
If none are specified, 20 transitions are selected. If there are more
than 20 possible transitions, the first 20 with frequencies between 70 GHz
and 500 GHz are selected. No more than 20 transitions may be written.
Default: program selects 20 transitions.

Key: print
Parameter which control level of printed output.
   0 = minimum output which is useful when running grids
   1 = normal output level
   2 = detailed output level - used for debugging and error checking

Key: log
Name of log file were full printed output for human consumption
is written. 

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