2009ApJ...702..414R

We measure the Ca II λ8542 line strength in 3360 stars along three lines of sight (LOS) in the Galactic bar: (l, b) ∼ (±5°.0, - 3°.5) and Baade's window, using Fabry-Pérot (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 λ8542 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 LOS. We present the stellar metallicity distributions along the major axis of the bar. We find the mean [Fe/H] = -0.09±0.04 dex in Baade's window, and the distribution in this field to agree well with previous works. We find gradients in the mean metallicity and its dispersion with respect to 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±0.10 dex, which is in agreement with recent measurements of Zoccali et al. This agreement demonstrates the reliability of our metallicity measurements.