metal abundance calibration of the ca(ii) triplet lines in rr lyrae stars

the gaia satellite is likely to observe thousands of rr lyrae stars with a small spectral range, between 8470 å to 8750 å, at a resolution of 11,500. in order to derive metallicity from gaia, we have obtained numerous spectra of rr lyrae stars at a resolution of 35,000 with the apache point observatory 3.5 m echelle spectrograph. we have correlated ca(ii) triplet line strengths with metallicity as derived from fe(ii) abundances, analogous to preston (astrophys. j., 130:507, 1959) use of the ca(ii) k line to estimate metallicity in rr lyrae stars.