RR Lyrae star metallicities from Caby photometry

Ten RR Lyr stars have been observed at different pulsational phases with Caby photoelectric photometry to calibrate the response of this system to RR Lyr metallicity. As has been done for nonvariable stars, the data are displayed in a color-color diagram of hk vs b-y, where hk=(Ca-b)-(b-y), It is found that the system is much more sensitive to metal abundance than the Stromgren mi index, and that the system retains good sensitivity even at the hottest phases of pulsation. The data produce lines of constant metallicity on the hk/b-y diagram which are single valued with respect to both b-y and hk. Therefore Caby photometry gives a metallicity which is independent of pulsational phase, a distinct advantage over Delta S and other techniques used to find RR Lyr abundances. This phase independence probably arises from the fact that Caby photometry is concerned largely with total absorption from the Ca K and H lines and the b-y continuum, and not the specific shapes of the hydrogen lines, which can be affected by changes in surface gravity as a function of phase in the pulsation and by emission near maximum light. The metallicity of the RRc star V753 Cen is determined to be -0.69+/-0.2 dex using the Caby technique. (C) 1996 American Astronomical Society.