Photometric molecular indices in warm carbon stars : NH, CN, CH, and C2

A ten-color photometric system for measuring band strengths of NH, CN, CH, and C2 molecules is described: the system is capable of distinguishing stars with unusual compositions from normal stars, of quantitatively differentiating among those stars, and of producing results consistent with spectroscopic data. Measurements for 26 R, CH, CH-like, and barium stars show that the C2 indices for CH and CH-like stars are similar to those of normal R stars. These kinds of stars have much stronger C2 indices than normal G-K giants, whereas the classical barium stars have C2 indices which are only slightly higher than in normal giants. The NH indices for the classical and marginal barium stars generally fall within the range of values of NH exhibited by giants of corresponding temperatures; the NH indices for many of the warm carbon stars are slightly lower than those for the normal giants. However, statistical analysis of the NH indices for the entire data set shows no significant difference between the warm carbon stars and normal giants.