The SpecFrame constructor function is particularly simple and a SpecFrame with default attributes is created as follows:
INCLUDE 'AST_PAR'
INTEGER SPECFRAME, STATUS
STATUS = 0
...
SPECFRAME = AST_SPECFRAME( ' ', STATUS )
Such a SpecFrame would represent the default coordinate system which is heliocentric wavelength in metres (i.e. wavelength corrected to take into account the Doppler shift caused by the velocity of the observer around the sun).
AST A Library for Handling World Coordinate Systems in Astronomy