Globular Cluster Metallicity Scale Based on the Abundance of Fe ii

Assuming that in the atmospheres of low-mass, metal-poor red giant stars, onedimensional models based on local thermodynamic equilibrium accurately predict the abundance of iron from Fe ii, we derive a globular cluster metallicity scale based on the equivalent widths of Fe ii lines measured from high resolution spectra of giants in 16 key clusters lying in the abundance range –2.4 < [Fe/H]II < –0.7. We base the scale largely on the analysis of spectra of 149 giant stars in 11 clusters by the Lick-Texas group supplemented by high-resolution studies of giants in five other clusters. We also derive ab initio the true distance moduli for certain key clusters (M5, M3, M13, M92, and M15) as a means of setting stellar surface gravities. Allowances are made for changes in the abundance scale if one employs: (1) Kurucz models with and without convective overshooting to represent giant star atmospheres in place of MARCS models and (2) the Houdashelt et al. color-temperature scale in place of the Alonso et al. scale. We find that [Fe/H]II is correlated linearly with , the reduced strength of the near infra-red Ca ii triplet defined by Rutledge et al., although the actual correlation coefficients depend on the atmospheric model employed. The correlations, limited to the range –2.4 < [Fe/H]II < –0.7 are as follows: present address: Astronomy Department, California Institute of Technology, Mail Stop 105-24, Pasadena, CA 91125; [email protected] Hubble Fellow