METHOD

        FIT\METHOD Arg [Parameters ...]

    Select the line profile for fits. Five type of profiles are available.

      - GAUSS     Select gaussian profiles.
        Up to 10 Gaussian, dependent or independent can be fitted in a spec-
        trum, according to command lines. Fitted parameters are:
            1) Area
            2) Velocity, and
            3) Width (FWHM)

      - SHELL     Horn-type profiles for Circumstellar Shells.
        Fitted parameters are:
            1) Area [K.MHz]
            2) Center offset [in MHz]
            3) Full Width at zero level, and
            4) Horn-to-center ratio (-1 for parabolic optically thick lines,
               0 for flat-topped lines, Infinity for perfectly double peaked
               lines).
        Profiles  are symmetric. Up to 10 dependent or independent lines may
        be fitted. X axis must be frequency.

      - NH3(1,1) or NH3(2,2) or NH3(3,3)
        Compute ammonia line profiles, with the assumptions of gaussian  ve-
        locity distribution and equal excitation temperatures. Fitted param-
        eters are:
            1) Main group opacity times ( Excitation temperature minus Back-
               ground temperature),
            2) Velocity,
            3) Width (FWHM = sqrt(8.0*alog(2.0)) * line 2nd order moment),
            4) Main group opacity.
        Up  to  10  independent lines may be fitted. The hyperfine structure
        description can be found in the structure HFS% right after the  com-
        mand METHOD is invoked.

      - HFS FileName    for HyperFine Structure
        This  is  very similar to the NH3 method, but the coefficients which
        describe the hyperfine structure are read in the file  FileName.  It
        must contain:
            - the number of hyperfine components (< 40, first line),
            - the  velocity offset and relative intensity (repeated for each
              component, one per line),
        The hyperfine structure description read from the this file  can  be
        found  in  the  structure HFS% right after the command METHOD is in-
        voked.  The fitted parameters are the same as for  the  NH3  method,
        except for the main group opacity.

        In the HFS method the main group opacity refers to the total opacity
        of the combined hyperfine components present in the description file
        divided  by the sum of their relative intensities. i.e. if the given
        relative intensities are normalised (their sum is 1)  the  resulting
        main group opacity will be the sum of the opacities of all hyperfine
        components present in the description file. This behaviour is useful
        for  example  in the case where we have only a part of the hyperfine
        components of a transition available in a spectrum. In this case one
        may  fit  only  the hyperfine components present on the spectrum and
        still recover the total opacity of the main transition.  The  safest
        way to avoid mistakes is to always use the statistical weight of the
        upper hyperfine level divided by the total statistical weight of the
        upper  level  of the main transition. In this manner one will always
        recover the total opacity of the main transition over all  hyperfine
        components.

      - ABSORPTION Filename   for hyperfine structures in absorption
        Fitted parameters are:
            1) One continuum level
        and for each line:
            2) Opacity
            3) Velocity, and
            4) Width (FWHM)

      - CONTINUUM [Width [Area_Ratio [Width_Ratio]]]  for Continuum drifts
        Fit  a  single gaussian and a linear baseline at the same time, with
        automatic determination of the parameters. Uses beam-switched infor-
        mation  for  two-component  fitting  if required. The command METHOD
        CONTINUUM accept additional arguments, which can be used to  custom-
        ize the fit:
            -  Width  is  the  width of the beam in arc seconds. By default,
              Width is a free parameter.
            - Area_Ratio is the reference to main beam area ratio, used  for
              beam-switch observing. By default, Area_Ratio is 1.
            -  Width_Ratio  is  the reference to main beam width ratio, used
              for beam-switch observing. By default, Width_Ratio is 1.
        A * can be used instead of a numerical value for each parameter, and
        indicates that the parameter is free.

    Note that in command LINES, one enters the peak line antenna temperature
    instead of the first variable in the guesses, except for  SHELL  method.
    Command LINES has no effect for CONTINUUM.

    CONTINUUM  and GAUSS methods only are relevant for continuum data, while
    GAUSS, SHELL, NH3, HFS and ABSORPTION methods can be used  for  spectro-
    scopic data.