Key points are not available for this paper at this time.
The DDO 51 filter has been added to the Washington photometric system. The strong surface gravity sensitivity of the Mg I "b" triplet and MgH bands which it monitors allows the system to easily discriminate between dwarfs and giants of late G and K spectral type. The system is especially suited as a membership criterion for abundance studies of distant cluster giants. The Mg index is insensitive to surface gravity variations among G giants. The metallicity sensitivity among giants is also relatively weak. Population I and II giants can be distinguished but no further differentiation is evident.
D. Geisler (Sat,) studied this question.