The relation between the two-dimensional classification established for the G and K stars and the MK classification is studied. It is shown that the giants and the dwarfs are well separated from each other and that the separation can be made complete if the criteria are complemented by the B-V colour. It is also found that the M giants can be classified quite accurately by means of the same criteria.
The connection between the spectrophotometric criteria and the intrinsic colours in the UBV system is investigated, and it is found that different relations hold for the dwarfs and the giants. The mean errors of typical B-V colour excess derived from the criteria and B-V are about +- 0.02 for the dwarfs to +-0.05 for the giants.
The absolute magnitudes of the late-type giants are discussed and a relation between the mean absolute magnitude in a volume of space and the spectrophotometric criteria is derived from astrometric data only (trigonometric parallaxes and proper motions in combination with radial velocities), The dispersion of the absolute magnitude is +-0.6.
Ge = m(4269) - m(4508)
Ce = m(4176) - m(4269)
Peak Filter wavelength Width [Å] [Å] 4508 4508 50 4269 4269 43 4176 4176 40All interference filter from Baird Atomic.