Jj. Claria et al., AN ABUNDANCE CALIBRATION FOR DDO PHOTOMETRY OF POPULATION-II G AND K GIANTS, Monthly Notices of the Royal Astronomical Society, 268(3), 1994, pp. 733-741
New photometry with the four primary filters of the DDO system is pres
ented for a sample of metal-poor giants with abundances determined fro
m high-dispersion spectroscopy. In addition, DDO photometry of very me
tal-deficient stars with photometric abundances is also given. These d
ata, combined with published DDO photometry of field and globular clus
ter stars, are used to establish an abundance calibration for Populati
on II giants. A new DDO index delta4548 is presented, which correlates
very well with [Fe/H], even for extremely metal-poor red giants ([Fe/
H] = -3.0). The present abundance calibration represents an improvemen
t over previous ones, because it exhibits less scatter and a more exte
nded range towards lower abundances. Iso-abundance lines have been det
ermined in the C0(45-48) versus C0(42-45) diagram and a new procedure
for determining abundances of Population II giants is described. Final
ly, the DDO abundance scale established here for globular clusters is
in good agreement with that of Zinn.