Examinando por Autor "Cohen, R. E."
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Ítem Infrared photometry and cat spectroscopy of globular cluster m 28 (ngc 6626)(EDP Sciences, 2021-04-01) Bidin, C. Moni; Mauro, F.; Contreras Ramos, R.; Zoccali, M.; Reinarz, Y.; Moyano, M.; González-Díaz, D.; Villanova, S.; Carraro, G.; Borissova, J.; Chené, A. N.; Cohen, R. E.; Geisler, D.; Kurtev, R.; Minniti, D.Context. Recent studies show that the inner Galactic regions host genuine bulge globular clusters, but also halo intruders, complex remnants of primordial building blocks, and objects likely accreted during major merging events. Aims. In this study we focus on the properties of M 28, a very old and massive cluster currently located in the Galactic bulge. Methods. We analysed wide-field infrared photometry collected by the VVV survey, VVV proper motions, and intermediate-resolution spectra in the calcium triplet range for 113 targets in the cluster area. Results. Our results in general confirm previous estimates of the cluster properties available in the literature. We find no evidence of differences in metallicity between cluster stars, setting an upper limit of Δ[Fe/H] < 0.08 dex to any internal inhomogeneity. We confirm that M 28 is one of the oldest objects in the Galactic bulge (13-14 Gyr). From this result and the literature data, we find evidence of a weak age-metallicity relation among bulge globular clusters that suggests formation and chemical enrichment. In addition, wide-field density maps show that M 28 is tidally stressed and that it is losing mass into the general bulge field. Conclusions. Our study indicates that M 28 is a genuine bulge globular cluster, but its very old age and its mass loss suggest that this cluster could be the remnant of a larger structure, possibly a primeval bulge building block.Ítem The vertical Na–O relation in the bulge globular cluster NGC 6553(Oxford University Press, 2020-01) Munoz, C; Villanova, S; Geisler, D; Cortes, C.C; Moni Bidin, C; Cohen, R. E.; Saviane, I; Dias, B; Tang, B; Mauro, FIn this article, we present a detailed chemical analysis of seven red giant members of NGC 6553 using high-resolution spectroscopy from VLT FLAMES. We obtained the stellar parameters (Teff, Log(g), vt, [Fe/H]) of these stars from the spectra, and we measured the chemical abundance for 20 elements, including light elements, iron-peak elements, α-elements, and neutron-capture elements. The metallicities in our sample stars are consistent with a homogeneous distribution. We found a mean of [Fe/H] = −0.14 ± 0.07 dex, in agreement with other studies. Using the α-elements Mg, Si, Ca, and Ti, we obtain the mean of [α/Fe] = 0.11 ± 0.05. We found a vertical relation between Na and O, characterized by a significant spread in Na and an almost non-existent spread in O. In fact, Na and Al are the only two light elements with a large intrinsic spread, which demonstrates the presence of multiple populations (MPs). An intrinsic spread in Mg is not detected in this study. The α, iron-peak, and neutron-capture elements show good agreement with the trend of the bulge field stars, indicating similar origin and evolution, in concordance with our previous studies for two other bulge globular clusters (NGC 6440 and NGC 6528).