The files in this directory specify standard chemical compositions and, optionally, grains.
One of these files will be used if the command
abundances "filename.abn"
appears.

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default "solar" composition
default.abn gives the default composition used if no others are specified.
default-backup.abn is a backup of this file, use to reestablish default if you change it
This is a fairly old set of "solar" abundances that we maintain for backwards compatibility

To change the default abundance set
replace the default.abn file with your own set of default abundances.
Copy default-backup.abn to default.abn to reestablish our default abundances

Available files

solar84.abn - abundances used by "old solar" option, used in versions 84-94
of the code.

Other .abn files - see the comments within the file for more details.
The file name gives a good indication of its contents

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Format of the *.abn files

comments begin with #

The file parsing ends with a line containing a field of stars, as
****************
Everything after the field of stars is ignored, so remaining lines can be used
to document the abundances, in addition to comment lines starting with #.

The grains command can be included.  The abundance files recognize all grain command options.
This makes it possible to include grains in your mix of gas and dust.

Names of elements are followed by the abundance by number relative to hydrogen.

Hydrogen may be in specified, or may not be.  If the abundance of hydrogen is 
given and is not equal to unity the code will rescale the abundances by the entered value 
for hydrogen.  If hydrogen is not specified it is assumed to have an abundance
of 1.

All elements heavier than hydrogen are turned off before the abn files are read.
An element is turned on if it appears in the abn file.
If an element is not included in the *.abn file it will not be included in the calculation.

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Original coding by Joshua Schlueter, NSF REU 2012 Summer
