Overview of directory files

The base directory of the source code contains the following text files by default:

• GN93hz: gives an overview of all currently available Rosseland-mean opacity tabulations from the OPAL project (126 tables in total). All tabulations assume solar abundances from Grevesse & Noels (1993).
• Y09800: example OPAL table for a pure helium atmosphere appropriate to model a wind outflows from classical Wolf-Rayet stars (hydrogen mass fraction $X=0$, helium mass fraction $Y=0.98$, metal mass fraction $Z=0.02$).

Generating new tables

Different Rosseland-mean opacity tabulations can be used in a radiation-hydrodynamic simulation. The procedure for using a different Rosseland-mean opacity tabulation than the provided Y09800 table is straightforward. First look up in the overview file GN93hz a suitable table, then copy its content into a new file, and save it accordingly in the current directory.

For example, when opacities from Table 92 are required, create a file with the following header in the current directory:

TABLE # 92     $G&N'93 Solar$     X=0.9000 Y=0.1000 Z=0.0000 dXc=0.0000 dXo=0.0000
 
                                                  log R
 
logT  -8.0   -7.5   -7.0   -6.5   -6.0   -5.5   -5.0   -4.5   -4.0   -3.5   -3.0   -2.5   -2.0   -1.5   -1.0   -0.5    0.0    0.5    1.0
 
3.75 -0.700 -0.870 -1.069 -1.281 -1.498 -1.711 -1.911 -2.078 -2.179 -2.182 -2.092 -1.936 -1.746 -1.539 -1.321 -1.097 -0.866 -0.629 -0.389
3.80 -0.473 -0.519 -0.606 -0.735 -0.889 -1.056 -1.217 -1.346 -1.422 -1.419 -1.337 -1.203 -1.026 -0.839 -0.639 -0.431 -0.214  0.013  0.244
3.85 -0.446 -0.445 -0.443 -0.445 -0.466 -0.514 -0.575 -0.630 -0.659 -0.639 -0.573 -0.462 -0.323 -0.164  0.008  0.197  0.391  0.602  0.820
3.90 -0.444 -0.440 -0.426 -0.390 -0.319 -0.217 -0.112 -0.020  0.054  0.120  0.192  0.281  0.391  0.508  0.645  0.804  0.972  1.156  1.351
......

It is important to not change the original file structure in order to avoid problems with reading in the table. In essence this means the newly created file containing a table should count 70 lines with different $log_{10}(T)$ values, as is standard for OPAL tables, and 19 columns with different $log_{10}(\rho)$ values. Additionally, the user can provide a custom directory, different from this AMRVAC directory, where such table files are stored (in the same format).

How-to

There are essentially two ways to use a (new) OPAL opacity table in a simulation.

1. When using the FLD module of the code, the filename containing the table can be passed as a string to the fld_opal_table variable within the fld_list namelist. By default the FLD module will use the already included Y09800 table.
2. When requiring the tables inside mod_usr.t the user needs to import some subroutines from mod_opal_opacity.t. Firstly, the table needs to be initialised by calling the subroutine init_opal_table. This should be done once, for example, inside the subroutine initglobaldata_usr. Secondly, to apply the values from the table to a given problem (e.g. boundary condition, source term computation), include a call to the subroutine set_opal_opacity. See mod_opal_opacity.t for what arguments these subroutines require in their calls. An example of how to call OPAL tables inside the mod_usr.t file is given by the Wolf-Rayet stellar wind test problems of the rhd module. (Note: these test problems also rely on the FLD module, but this is not a prerequisite to use the tables.)