We measure the Ca ii \lambda 8542  line strength in 3360 stars along three lines-of-sight in the Galactic bar : ( l,b ) \sim ( \pm 5.0 , -3.5 ) ° and Baade ’ s Window , using FP absorption line spectroscopy .
This is the first attempt to show that reliable absorption line strengths can be measured using FP spectroscopy .
The Ca ii \lambda 8542 Â line is a good indicator of metallicity and its calibration to [ Fe/H ] is determined for globular cluster red giants in previous investigations .
We derive such a calibration for the bulge giants and use it to infer metallicities for our full red clump sample ( 2488 stars ) at all three lines-of-sight .
We present the stellar metallicity distributions along the major axis of the bar .
We find the mean \mathrm { [ Fe / H ] } = -0.09 \pm 0.04 dex in Baade ’ s Window , and find the distribution in this field to agree well with previous works .
We find gradients in the mean metallicity and its dispersion w.r.t Baade ’ s WIndow of -0.45 and -0.20 dex respectively at l = +5.5 ° and of -0.10 dex and -0.20 dex at l = -5.0 ° .
We detect a signature of a possible tidal stream at l = +5.5 ° , in both our velocity and metallicity distributions .
Its radial velocity indicates that it is not associated with the Sagittarius stream .
We also measure the metallicity of a bulge globular cluster NGC 6522 in our Baade ’ s Window field to be -0.90 \pm 0.10 dex , in agreement with recent measurements of Zoccali et al .
( 46 ) .
This agreement demonstrates the reliability of our metallicity measurements .