A Metallicity Calibration Using {\it hk}/({\it b-y}) Photometry for the Warmer Phases of RR Lyr Stars
Session 101 -- Intrinsic Variables
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

## [101.02] A Metallicity Calibration Using {\it hk}/({\it b-y}) Photometry for the Warmer Phases of RR Lyr Stars

Scott R. Baird and Jeffrey W. Deane (Benedictine College and U. Kansas)

The byCa filter system was used to obtain hk and b-y colors for a dozen RR Lyr stars at various phases, where hk = (Ca - b ) - (b - y ). When the data are plotted in an hk /(b-y ) color-magnitude diagram there is a clear stratification of the data points by metallicity, with the lower metallicity stars having a lower value of hk . In the color range 0.10<b-y <0.25 the metallicity depends on hk only. The empirical relation is determined to be [Fe/H] = 12.5(hk - 0.40). The hk index is shown to be substantially more sensitive to metallicity than the Stromgren $m_1$ index for these stars, confirming previous predictions. Because hk has already been shown to be more sensitive to metallicity than $m_1$ for cooler stars, the hk index has now been shown to be quite sensitive to metallicity over a substantial range of temperature.