model

The model option allows the user to input parameters for up to 20 circular or elliptical gaussian source model components. The initial source model is read in from the model.dat file. If this option is chosen, a screen showing a series of bars going from left to right is displayed. Each bar contains 9 segments showing different aspects of the input source model. The user can use the arrow keys to move the cursor (light tan or yellow) across each segment. The segment that is currently highlighted can then be modified simply by typing in the new value and hitting return. The model parameters are in the following order:

• 1. X position from phase center in milliarcseconds.
• 2. Y position from phase center in milliarcseconds.
• 3. The component flux in millijanskys.
• 4. The FWHM along the major axis in milliarcseconds.
• 5. The FWHM along the minor axis in milliarcseconds.
• 6. The position angle of the major axis measured from north toward east.
• 7. The percentage polarization of the component.
• 8. The position angle of the polarization vector measured from north toward east.

All of these values can be modified as desired. The last value in each row of segments is the calculated brightness temperature of that component in Kelvin. If a component size of 0 is entered for the major and minor axes then a dash is displayed to indicate that the brightness temperature is undefined.

In order to add a component to the source model, the `F1' key must be pressed. This will cause a new row of segments to appear below the last compenent. The source parameter values default automatically to 0.0 and the user must then enter the desired values. A comonent may be removed by pressing the Delete key when the highlighting bar is lying somewhere in the row corresponding to the component to be removed. The source model input may be saved by pressing `F2', which automatically writes the displayed model into the model.dat file. The user may also modify model.dat directly using an editor. If new model components input from the screen are saved, the old model.dat file is overwritten. See Figure on p. .