Chemical and kinematical properties of galactic bulge stars surrounding the stellar system Terzan 5

As part of a study aimed at determining the kinematical and chemical proper- ties of Terzan 5, we present the first characterization of the bulge stars surround- ing this puzzling stellar system. We observed 615 targets located well beyond the tidal radius of Terzan 5 and we found that their radial velocity distribution is well described by a Gaussian function peaked at = +21.0±4.6 kms −1 and with dispersionv = 113.0 ± 2.7 kms −1 . This is the one of the few high- precision spectroscopic survey of radial velocities for a large sample of bulge stars in such a low and positive latitude environment (b=+1.7°). We found no evi- dence for the peak at ∼ +200 kms −1 found in Nidever et al. (2012). The strong contamination of many observed spectra by TiO bands prevented us from deriving the iron abundance for the entire spectroscopic sample, introducing a selection bias. The metallicity distribution was finally derived for a sub-sample of 112 stars in a magnitude range where the effect of the selection bias is neg- ligible. The distribution is quite broad and roughly peaked at solar metallicity ((Fe/H)≃ +0.05 dex) with a similar number of stars in the super-solar and in the sub-solar ranges. The population number ratios in different metallicity ranges agree well with those observed in other low-latitude bulge fields suggesting (i) the possible presence of a plateau for |b| < 4° for the ratio between stars in the