MODELDATA.DAT (1)

This is created by the astra.tcl program and contains most of the parameters describing the model to be run. The file is 21 lines long and contains the following information (in order):

• object - the name of the object being studied. This should be a series of characters without spaces as it will be used as the extension for the OBJECTDATA.*** file.

• molecule - the molecule being modelled. This is used as the extension for the MOLECDATA.*** file.

• telescope - the telescope used. This is used as the extension for the TELEDATA.*** file.

• transitions to be modelled - these are a series of 5 pairs of 2 numbers (ie. 10 in total) that represent the upper and lower levels (respectively) of the transitions to be calculated. eg. 2 1 3 2 0 0 0 0 0 0 will output for transitions 2 $\rightarrow$1 and 3 $\rightarrow$2 - the zeros are ignored by the program (although they must be present). The list is stored in the array tr with the i$^{th}$ transition having its upper level in tr(1,i) and its lower level in tr(2,i). Clearly the maximum number of transitions that can be output by a single model is 5.

• helium correction, convergence criteria - the helium correction is a factor by which the collision coefficients are multiplied in order to account for the presence of Helium atoms as well as H$_2$ molecules. The convergence criteria is a number such that convergence is defined to have occurred when the source function (denoted by array `s' in the program) satisfies:
  
  $$\frac{S_{this~iteration}-S_{last~ iteration}}{S_{this~iteration}} \le convergence~criteria$$
  
  

• Number of output positions - This is the number of positions for which output is to be calculated for each of the transitions. ie. The first number is the number of output positions for the first transitions, the second number is the number of output positions for the second transition, etc.

• The output positions - For each transition there are a pair of lines giving (in vertical pairs) the co-ordinates of the output positions. The number of these that are read in is determined by the value given in the line described above as `Number of output positions'. For each transition there can be a maximum of 50 output positions. The positions are given in arcseconds.

• eangle, rangle - These describe the viewing angle of the cloud. eangle is the position of the observer relative to the disk that passes through the centre of the cloud. A value of 0 represents an observer looking into the cloud along the plane of the central disk and a value of 90 represents an observer looking down the centre line of the cloud parallel to the cylinders. The value is given in degrees. rangle describes the tilt of the cloud relative to the observer. These are described in detail in section 4.8.1.

• number of gridding points - The number of gridding points must be an odd integer and represents the number of gridding points used in the convolution.

• hlines - A measure of the number of lines of sight to be used in the cloud.

• velsteps - The number of velocity steps to use whilst calculating the radiation field in the cloud.

• outpoints - The number of velocity points across the line profiles that are calculated for output.