The Hubble Space Telescope UV Legacy Survey of Galactic globular clusters – IX. The Atlas of multiple stellar populations

By A. Milone, G. Piotto, A. Renzini, A. Marino, L. Bedin, Enrico Vesperini, F. D’Antona, D. Nardiello, Jay Anderson, I. King and 10 more. 2016

301 citations recorded by the source corpus.

We use high-precision photometry of red-giant-branch (RGB) stars in 57 Galactic globular clusters (GCs), mostly from the 'Hubble Space Telescope (HST ) UV Legacy Survey of Galactic GCs', to identify and characterize their multiple stellar populations. For each cluster the pseudo-two-colour diagram (or 'chromosome map') is presented, built with a suitable combination of stellar magnitudes in the F275W, F336W, F438W, and F814W filters that maximizes the separation between multiple populations. In the chromosome map of most GCs (type-I clusters), stars separate in two distinct groups that we identify with the first (1G) and the second generation (2G). This identification is further supported by noticing that 1G stars have primordial (oxygen-rich, sodium-poor) chemical composition, whereas 2G stars are enhanced in sodium and depleted in oxygen. This 1G-2G separation is not possible for a few GCs where the two sequences have apparently merged into an extended, continuous sequence. In some GCs (type-II clusters) the 1G and/or the 2G sequences appear to be split, hence displaying more complex chromosome maps. These clusters exhibit multiple subgiant branches (SGBs) also in purely optical colour-magnitude diagrams, with the fainter SGB joining into a red RGB which is populated by stars with enhanced heavy-element abundance. We measure the RGB width by using appropriate colours and pseudo-colours. When the metallicity dependence is removed, the RGB width correlates with the cluster mass. The fraction of 1G stars ranges from ~8 per cent to ~67 per cent and anticorrelates with the cluster mass, indicating that incidence and complexity of the multiple population phenomenon both increase with cluster mass.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/366556b820ddca2dea44a83f7023371e1d977718

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Jo Bovy
2. Hans-Walter Rix
3. H. Baumgardt
4. S. Majewski
5. J. Holtzman
6. M. Shetrone
7. D. Nidever
8. Michael Hilker

In Atomic and Molecular Physics, and Optics

1. K. Covey
2. B. Andrews
3. Jo Bovy
4. S. Majewski
5. M. Shetrone
6. J. Tayar

In Instrumentation

1. Michael Hilker
2. S. Majewski
3. D. Nidever
4. N. Neumayer
5. Jo Bovy
6. J. Holtzman
7. H. Baumgardt
8. J. Simon

Citations in the corpus

• Target Selection for the SDSS-IV APOGEE-2 Survey (2017, background): “Despite this, globular clusters are known to generally host multiple stellar populations (e.g., Milone et al. 2017), with wellcharacterized patterns in certain elemental abundances (see Gratton et al. 2012, for a review).”
• A catalogue of masses, structural parameters, and velocity dispersion profiles of 112 Milky Way globular clusters (2018, background): “It can be seen that the fraction of first generation stars anti-correlates strongly with either the cluster mass (confirming the results found by Milone et al. 2017) or the central escape velocity.”
• Nuclear star clusters (2009, background): “An overlapping set of clusters show colormagnitude and color-color diagrams similar to that of ω Cen, also suggesting metallicity spreads (Type II clusters in Milone et al. 2017).”
• A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808 (2019, methodology): “The mF336W − mF438W color provides a clear distinction between the population 1 and 2 stars as defined by Milone et al. (2017).”