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The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XII. The RGB bumps of multiple stellar populations

Lagioia, EP, Milone, AP, Marino, AF, Cassisi, S, Aparicio, AJ, Piotto, G, Anderson, J, Barbuy, B, Bedin, LR, Bellini, A, Brown, T, D'Antona, F, Nardiello, D, Ortolani, S, Pietrinferni, A, Renzini, A, Salaris, M, Sarajedini, A, van der Marel, R and Vesperini, E (2018) The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XII. The RGB bumps of multiple stellar populations. Monthly Notices of the Royal Astronomical Society, 475 (3). pp. 4088-4103. ISSN 0035-8711

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Abstract

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters is providing a major breakthrough in our knowledge of globular clusters (GCs) and their stellar populations. Among the main results, we discovered that all the studied GCs host two main discrete groups consisting of first generation (1G) and second generation (2G) stars. We exploit the multiwavelength photometry from this project to investigate, for the first time, the Red Giant Branch Bump (RGBB) of the two generations in a large sample of GCs. We identified, with high statistical significance, the RGBB of 1G and 2G stars in 26 GCs and found that their magnitude separation as a function of the filter wavelength follows comparable trends. The comparison of observations to synthetic spectra reveals that the RGBB luminosity depends on the stellar chemical composition and that the 2G RGBB is consistent with stars enhanced in He and N and depleted in C and O with respect to 1G stars. For metal-poor GCs the 1G and 2G RGBB relative luminosity in optical bands mostly depends on helium content, Y. We used the RGBB observations in F606W and F814W bands to infer the relative helium abundance of 1G and 2G stars in 18 GCs, finding an average helium enhancement ΔY = 0.011 ± 0.002 of 2G stars with respect to 1G stars. This is the first determination of the average difference in helium abundance of multiple populations in a large number of clusters and provides a lower limit to the maximum internal variation of helium in GCs. © 2017 The Authors.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Date Deposited: 11 May 2018 10:21
Last Modified: 11 May 2018 10:21
DOI or Identification number: 10.1093/mnras/sty083
URI: http://researchonline.ljmu.ac.uk/id/eprint/8644

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