The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XX. Ages of single and multiple stellar populations in seven bulge globular clusters

23 Jan 2020  ·  Oliveira R. A. P., Souza S. O., Kerber L. O., Barbuy B., Ortolani S., Piotto G., Nardiello D., Pérez-Villegas A., Maia F. F. S., Bica E., Cassisi S., D'Antona F., Lagioia E., Libralato M., Milone A. P., Anderson J., Aparicio A., Bedin L. R., Brown T. M., King I. R., Marino A. F., Pietrinferni A., Renzini A., Sarajedini A., van der Marel R., Vesperini E. ·

In the present work we analyzed seven globular clusters selected from their location in the Galactic bulge and with metallicity values in the range $-1.30\lesssim\rm{[Fe/H]}\lesssim-0.50$. The aim of this work is first to derive cluster ages assuming single stellar populations, and secondly, to identify the stars from first (1G) and second generations (2G) from the main sequence, subgiant and red giant branches, and to derive their age differences... Based on a combination of UV and optical filters used in this project, we apply the Gaussian mixture models to distinguish the multiple stellar populations. Applying statistical isochrone fitting, we derive self-consistent ages, distances, metallicities, and reddening values for the sample clusters. An average of $12.3\pm0.4$ Gyr was obtained both using Dartmouth and BaSTI (accounting atomic diffusion effects) isochrones, without a clear distinction between the moderately metal-poor and the more metal-rich bulge clusters, except for NGC 6717 and the inner halo NGC 6362 with $\sim 13.5$ Gyr. We derived a weighted mean age difference between the multiple populations hosted by each globular cluster of $41\pm170$ Myr adopting canonical He abundances; whereas for higher He in 2G stars, this difference reduces to $17\pm170$ Myr, but with individual uncertainties of $500$ Myr. read more

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Astrophysics of Galaxies Solar and Stellar Astrophysics