datakey.sten (13)

The first line contains just a number that represents the number of different models in the file. There must be at least one model in the file. The rest of the file consists of all the stored models. The models are separated in the file by a series of dashes - these are purely an aid for viewing the file and are ignored by the program. As such this line could be used to add a short note about a model - although it could not be more than 60 characters long. Each entry has 14 lines with the following information:

• model number - a unique identifying number for each model. The output from this model is stored in the Runs subdirectory in a file called run.xyz where xyz is the model number in 3 digit form (eg. the output from model number 4 is found in /Runs/run.004). This restricts the maximum number of models to 999.

• 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, sten - 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:
  

  $$\frac{S_{this~iteration}-S_{last~ iteration}}{S_{this~iteration}} \le convergence~criteria$$ (4.4)

  
  

  Sten is a variable that is no longer used.

• inner cutoff, number of gridding points - the inner cutoff is the shell number within which the molecular abundance is held constant (eg. a value of 3 will hold the molecular abundance constant at the value on the boundary of shells 3 and 4).

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

• number of shells, innermost shell, cloud radius - the number of shells up to a maximum of 30. The innermost shell radius in pc, the cloud radius (ie. outermost shell radius) in pc.

• avs, gvs, bvs, evs, fvs - the shell velocities in ${\rm km} \, {\rm s}^{-1}$. The 5 numbers are combined in the following manner:
  
  $$V_{shell}=(avs) e^{-(bvs) r^2} r^{gvs} + (evs) r^{fvs}$$
  
  
  where $r$ is the normalised shell radius (ie. $r=\frac{r_{shell}}{r_{cloud}}$)

• ah2, gh2, bh2, eh2, fh2 - shell hydrogen densities. The parameters are combined as above for the shell velocities.

• atk, gtk, btk, etk, ftk - shell kinetic temperatures. The parameters are combined as above for the shell velocities.

• ano, gno, bno, eno, fno - shell molecular abundances. The parameters are combined as above for the shell velocities.

• avt, gvt, bvt, evt, fvt - shell turbulent velocities. The parameters are combined as above for the shell velocities.

• number of positions, position 1, position 2, ..., position 5 - the number of positions for which output is to be generated including the centre. The position numbers, of which there may be a maximum of 5, are the step sizes for each transition to be output. For example the if the model is to output the 2 $\rightarrow$1 and 3 $\rightarrow$2 transitions at 4 positions with (position 1) = 20 and (position 2) = 15 then output will be calculated at 0 $^{\prime \prime}$, 20 $^{\prime \prime}$, 40 $^{\prime \prime}$ and 60 $^{\prime \prime}$ for the 2 $\rightarrow$1 transition (ie. 4 positions) and at 0 $^{\prime \prime}$, 15 $^{\prime \prime}$, 30 $^{\prime \prime}$, 45 $^{\prime \prime}$ for the 3 $\rightarrow$2 transition (ie. again 4 positions).

There is no actual need in normal use for the user to have anything to do with this file as the program makes all necessary changes itself, including adding new entries and deleting unwanted ones.