Medium resolution ( R = 4000 - 9000 ) spectra of the near infrared Ca ii lines ( at 8498 , 8542 , and 8662 Å ) in M31 globular cluster integrated light spectra are presented .
In individual stars the Ca ii triplet ( CaT ) traces stellar metallicity ; this paper compares integrated CaT strengths to well determined , high precision [ Fe/H ] values from high resolution integrated light spectra .
The target globular clusters cover a wide range in metallicity ( from [ Fe / H ] \sim - 2.1 to -0.2 ) .
While most are older than \sim 10 Gyr , some may be of intermediate age ( 2-6 Gyr ) .
A handful ( 3-6 ) have detailed abundances ( e.g .
low [ Ca/Fe ] ) that indicate they may have been accreted from dwarf galaxies .
Using various measurements and definitions of CaT strength , it is confirmed that for GCs with [ Fe / H ] \la - 0.4 and older than \sim 2 Gyr the integrated CaT traces cluster [ Fe/H ] to within \sim 0.2 dex , independent of age .
CaT lines in metal rich GCs are very sensitive to nearby atomic lines ( and TiO molecular lines in the most metal rich GCs ) , largely due to line blanketing in continuum regions .
The [ Ca/Fe ] ratio has a mild effect on the integrated CaT strength in metal poor GCs .
The integrated CaT can therefore be safely used to determine rough metallicities for distant , unresolved clusters , provided that attention is paid to the limits of the measurement techniques .