Intermediate-band photometry of late-type stars. V. Calibration of indices.

Additional data for several stellar groups and clusters are used to improve a previously determined provisional relation between M₁ photometric index and the parameter /Fe/H/(solar) as well as to test the usefulness of the C₁ photometric index for luminosity determinations. The data are for 43 members of the Wolf 630 group, 14 members of the 61 Cygni group, 30 members of the Arcturus group, 14 members of Kapteyn's star groups, and various members of the Hyades, 47 Tuc, NGC2420, Omega Cen, and an anonymous group of subdwarfs. It is found that in general the values of C₁ only confirm a giant or dwarf classification without yielding accurate luminosities and that the main contribution of C₁ for disk objects is in isolating peculiar stars. The results also indicate that there is a luminosity effect in M₁ for the strongest-lined stars and that the values of M₁ become distorted, probably by the presence of TiO, for R-I larger than about +0.5 magnitude. An array for interpolating /FE/H/(solar) from (R-I, M₁₎ is constructed by adopting mean values of /Fe/H/(solar) equal to +0.1,-0.35, -0.6, and -1.8 for the Hyades, Wolf 630, Arcturus, and Kapteyn's star groups, respectively.