The Correlations between the Intrinsic Colors and Spectroscopic
  Metallicities of M31 Globular Clusters
  We present the correlations between the spectroscopic metallicities and
ninety-three different intrinsic colors of M31 globular clusters, including
seventy-eight BATC colors and fifteen SDSS and near infrared ugrizK colors. The
BATC colors were derived from the archival images of thirteen filters (from c
to p), which were taken by Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor
Sky Survey with a 60/90 cm f/3 Schmidt telescope. The spectroscopic
metallicities adopted in our work were from literature. We fitted the
correlations of seventy-eight different BATC colors and the metallicities for
123 old confirmed globular clusters, and the result implies that correlation
coefficients of twenty-three colors r>0.7. Especially, for the colors
$(f-k)_0$, $(f-o)_0$, and $(h-k)_0$, the correlation coefficients are r>0.8.
Meanwhile, we also note that the correlation coefficients (r) approach zero for
$(g-h)_0$, $(k-m)_0$, $(k-n)_0$, and $(m-n)_0$, which are likely to be
independent of metallicity. Similarity, we fitted the correlations of
metallicity and ugrizK colors for 127 old confirmed GCs. The result indicates
that all these colors are metal-sensitive (r>0.7), of which $(u-K)_0$ is the
most metal-sensitive color. Our work provides an easy way to simply estimate
the metallicity from colors.
