SHOW SED [Frequency [FileName]]
Display the SED, computed by the "SED" widget from images (using the
FLUX command) or from UV Tables (by fitting a simple model using
UV_FIT), and fit a simple power law model through it.
Frequency is the reference frequency in GHz at which the flux is comput-
ed.
FileName is the data file produced by the "SED" widget.
If Frequency or Filename are not specified, their last values are re-
used.