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ABSTRACT This is the third paper in a series that attempts to observe a clear signature of the Galactic bar/bulge using kinematic observations of the bulge stellar populations in low foreground extinction windows. We report on the detection of ∼100 000 new proper motions in four fields covering the far side of the Galactic bar/bulge, at negative longitudes. Our proper motions have been obtained using observations from the Advance Camera for Surveys (ACS), on board of the Hubble Space Telescope (HST), with a time-baseline of 8–9 years, which has produced accuracies better than 0.5 mas yr−1 for a significant fraction of the stellar populations with F814W < 23 mag. Interestingly, as shown in previous works, the Hess diagrams show a strikingly similar proper motion distribution to fields closer to the Galactic center and consistent with an old stellar population. The observed kinematics point to a significant bulge rotation, which seems to predominate even in fields as far as l ≃ −8°, and is also reflected in the changes of the velocity ellipsoid in the l, b plane as a function of distance. 

ABSTRACT This study presents the results concerning six red giant stars members of the globular cluster NGC 6558. Our analysis utilized high-resolution near-infrared spectra obtained through the CAPOS initiative (the APOgee Survey of Clusters in the Galactic Bulge), which focuses on surveying clusters within the Galactic Bulge, as a component of the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2). We employ the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code to provide line-by-line elemental-abundances for Fe-peak (Fe, Ni), α-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Al), and the s-process element (Ce) for the four stars with high-signal-to-noise ratios. This is the first reliable measure of the CNO abundances for NGC 6558. Our analysis yields a mean metallicity for NGC 6558 of 〈[Fe/H]〉 = −1.15 ± 0.08, with no evidence for a metallicity spread. We find a Solar Ni abundance, 〈[Ni/Fe]〉 ∼ +0.01, and a moderate enhancement of α-elements, ranging between +0.16 and <+0.42, and a slight enhancement of the s-process element 〈[Ce/Fe]〉 ∼ +0.19. We also found low levels of 〈[Al/Fe]〉 ∼ +0.09, but with a strong enrichment of nitrogen, [N/Fe] > +0.99, along with a low level of carbon, [C/Fe] < −0.12. This behaviour of Nitrogen-Carbon is a typical chemical signature for the presence of multiple stellar populations in virtually all GCs; this is the first time that it is reported in NGC 6558. We also observed a remarkable consistency in the behaviour of all the chemical species compared to the other CAPOS bulge GCs of the same metallicity. 

Abstract The Milky Way Bulge extra-tidal star survey is a spectroscopic survey with the goal of identifying stripped globular cluster stars from inner Galaxy clusters. In this way, an indication of the fraction of metal-poor bulge stars that originated from globular clusters can be determined. We observed and analyzed stars in and around BH 261, an understudied globular cluster in the bulge. From seven giants within the tidal radius of the cluster, we measured an average heliocentric radial velocity of 〈RV〉 = −61 ± 2.6 km s⁻¹with a radial velocity dispersion of 〈σ〉 = 6.1 ± 1.9 km s⁻¹. The large velocity dispersion may have arisen from tidal heating in the cluster’s orbit about the Galactic center, or because BH 261 has a high dynamical mass as well as a high mass-to-light ratio. From spectra of five giants, we measure an average metallicity of 〈[Fe/H]〉 = −1.1 ± 0.2 dex. We also spectroscopically confirm an RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 ± 0.4 kpc. Stars with 3D velocities and metallicities consistent with BH 261 reaching to ∼0.°5 from the cluster are identified. A handful of these stars are also consistent with the spatial distribution of potential debris from models focusing on the most recent disruption of the cluster. 

ABSTRACT We present photometric metallicity measurements for a sample of 2.6 million bulge red clump stars extracted from the Blanco DECam Bulge Survey (BDBS). Similar to previous studies, we find that the bulge exhibits a strong vertical metallicity gradient, and that at least two peaks in the metallicity distribution functions appear at b < −5°. We can discern a metal-poor ([Fe/H] ∼ −0.3) and metal-rich ([Fe/H] ∼ +0.2) abundance distribution that each show clear systematic trends with latitude, and may be best understood by changes in the bulge’s star formation/enrichment processes. Both groups exhibit asymmetric tails, and as a result we argue that the proximity of a star to either peak in [Fe/H] space is not necessarily an affirmation of group membership. The metal-poor peak shifts to lower [Fe/H] values at larger distances from the plane while the metal-rich tail truncates. Close to the plane, the metal-rich tail appears broader along the minor axis than in off-axis fields. We also posit that the bulge has two metal-poor populations – one that belongs to the metal-poor tail of the low latitude and predominantly metal-rich group, and another belonging to the metal-poor group that dominates in the outer bulge. We detect the X-shape structure in fields with |Z| > 0.7 kpc and for stars with [Fe/H] > −0.5. Stars with [Fe/H] < −0.5 may form a spheroidal or ‘thick bar’ distribution while those with [Fe/H] $$\gtrsim$$ −0.1 are strongly concentrated near the plane.