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

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 $\Delta$Y=0.011$\pm$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.

16 pages, 11 figures, 2 tables. Accepted for publication in MNRAS

References in corpus (14)

• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• New Grids of ATLAS9 Model Atmospheres
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• On the self-enrichment scenario of galactic globular clusters: Constraints on the IMF
• Multiple stellar populations in Magellanic Clouds clusters. I. An ordinary feature for intermediate age globulars in the LMC?
• Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
• Ground-Based CCD Astrometry with Wide Field Imagers. I. [Observations just a few years apart allow decontamination of field objects from members in two Globular clusters.]
• Iron and neutron-capture element abundance variations in the globular cluster M2 (NGC 7089)
• Nitrogen abundances in giant stars of the globular cluster NGC 6752
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. II. The seven stellar populations of NGC7089 (M2)
• A large C+N+O abundance spread in giant stars of the globular cluster NGC 1851
• A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19)
• Red Giant Branch Bump Star Counts in Data and Stellar Models

Cited by in corpus (6)

• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XIX. A Chemical Tagging of the Multiple Stellar Populations Over the Chromosome Maps
• The Relationship Between Globular Cluster Mass, Metallicity, and Light Element Abundance Variations
• A Deep View of a Fossil Relic in the Galactic Bulge: The Globular Cluster HP1
• Four stellar populations and extreme helium variation in the massive outer-halo globular cluster NGC 2419
• Mass loss of different stellar populations in Globular Clusters: the case of M4
• Multiple stellar populations of globular clusters from homogeneous Ca--CN photometry. III. NGC 6752