THE MOUNT-WILSON-OBSERVATORY METALLICITY INDEX, CRV - COMPARISON WITHOTHER PHOTOMETRIC SYSTEMS

A new spectrophotometric index, C(RV), is assessed as a metallicity in dicator for late-type stars. The index is the ratio of the measured ph otospheric fluxes in 20 angstrom wide passbands centered at 4001 and 3 901 angstrom. C(RV) correlates directly with the metallicity index, m1 , of the Stromgren uvby system and with the metallicity index hk, of A nthony-Twarog et al. (1991). Using observations of 236 dwarfs and 140 giants combined with stellar atmosphere models (Kurucz 1991), we compa red the sensitivity of the C(RV) m1, and hk indices to metal abundance . We also studied the sensitivity of the C(RV), c1, and hk indices to surface gravity. The effect of interstellar extinction on all the indi ces was also studied from published mean extinction laws. We find that the C(RV) index is sensitive to the variation of metal abundance, [M] , over the range examined (- 5.0 less than or similar to [M] less than or similar to 0.5). C(RV) is also more sensitive than the m, index at metal-poor conditions ([M] less than or similar to - 2.0). The C(RV) index has the following advantages: (1) the passbands of C(RV) are dom inated by Fe lines, which reduce the uncertainty that may be introduce d by the presence of lines of alpha-process elements with enhanced abu ndances at metal-poor conditions; (2) the effect of interstellar redde ning is limited because the two passbands are separated in wavelength by only 100 angstrom. We also find that the atmospheric models produce results that agree qualitatively with the trends of observed indices on stellar parameters such as effective temperature, metallicity, and surface gravity.