CPPSIMU – cloud description

Definition of 1D cloud model

One-dimensional, spherically symmetric model cloud can be defined in two ways. The first is to specify analytical formulas for the various parameters. For example:

 spheres 30
 # models a + b * (radius^c); radius = radius_of_the_sphere/radius_of_the_cloud
 density     1.0  0.0  0.0
 temperature 1.0  0.0  1.0
 turbulence  1.0  0.0  0.0
 radial      0.0 -1.0  1.0
 rotation    0.0  0.0  0.0
 fraction    1.0  0.0  0.0
 expo 1.0
 hole 0.1

The file can be called anything, e.g. sample.cloud. The first line gives the number of spheres. The following lines specify density etc. using three parameters a, b, and c listed on the line. The functional form of the distributions is a+b*r^c, where r is radius relative to the outer radius of the model cloud. The parameter expo determines how the cloud is divided into shells. Radiae are first calculated equidistantly and are then raised to the power given by expo. For example, if file contained line expo 0.33 the shells would have roughly equal volumes. The parameter hole specifies an empty innermost shell. The radius of the first, empty shell is adjusted to that radius.

Alternatively, the values can be listed shell by shell and the file looks like this:

 4.000e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00
 6.179e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00
 7.082e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00
 7.775e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00
 8.359e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00
 8.873e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00
 9.339e+16 1.000e+05 1.000e+01 5.000e-09 1.500e-01 0.000e+00 0.000e+00

The first line indicates that values are read from the file directly (not computed) and the number of shells is given on the second line. The following lines list for each shell (starting from the centre) the values: outer radius, density cm-3, temperature K, fractional abundance, turbulent linewidth [km/s], radial velocity [km/s], and velocity of cloud rotation [km/s].

In both cases the ini-file should contain a line cloud1d sample.cloud (or whatever the previous files were called). All parameters can also be re-scaled using appropriate keywords in the ini-file: abundance, density, sigma, and velocity. The actual radius of the cloud is always determined by the keywords distance and angle (or the keyword size).

Definition of a 3D cloud

The 3D cloud consists of a cartesian grid and the cloud is divided into Nx  × Ny  ×  Nz cubic cells. The cloud is defined by giving a file that lists the required parameters (density etc.) cell by cell. The cloud can be either a plain binary file or a FITS file.

Binary file

This may be the simplest alternative. A binary file starts with three integers (3 x 4 bytes) that give the dimensions of the cloud: Nx, Ny, Nz. This is followed by floating point numbers (4 bytes each). The cloud is gone through cell by cell (x-coordinate runs fastest), and for each cell the file contains seven consecutive floating point numbers. These give for this cell the values of
density [cm^-3], kinetic temperature [K], turbulent linewidth [km/s], three components of velocity vector [km/s], and the fractional abundance. Note that all these values can still be scaled using various keywords in the ini-file.


The 3D cloud can be given as a 4-dimensional FITS file. NAXIS1 equals 6 or 7, and the fields are the same (density etc.) as for the binary file (NAXIS1=7) or the fractional abundance can be omitted (NAXIS1=6). The three remaining axes correspond to cloud dimensions Nx, Ny, Nz.