METHOD

FIT\METHOD Arg [Parameters ...] Select the line profile for fits. Five type of profiles are available. - GAUSS Select gaussian profiles. Up to 5 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 5 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 3 independent lines may be fitted. The hyperfine structure de- scription can be found in the structure HFS% right after the command 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 NH3 method. - 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 cus- tomize 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.

Gildas manager 2018-05-23