Historically, multiple populations in globular clusters (GCs) have been mostly studied from ultraviolet and optical filters down to stars that are more massive than ∼0.6 M⊙. Here, we exploit deep near-infrared (NIR) photometry from the Hubble Space Telescope to investigate multiple populations among M-dwarfs in the GC NGC 6752. We discovered that the three main populations (A, B, and C), previously observed in the brightest part of the colour-magnitude diagram (CMD), define three distinct sequences that run from the main-sequence (MS) knee towards the bottom of the MS (∼0.15 M⊙). These results, together with similar findings on NGC 2808, M 4, and ω Centauri, demonstrate that multiple sequences of M-dwarfs are common features of the CMDs of GCs. The three sequences of low-mass stars in NGC 6752 are consistent with stellar populations with different oxygen abundances. The range of [O/Fe] needed to reproduce the NIR CMD of NGC 6752 is similar to the oxygen spread inferred from high-resolution spectroscopy of red giant branch (RGB) stars. The relative numbers of stars in the three populations of M-dwarfs are similar to those derived among RGB and MS stars more massive than ∼0.6 M⊙. As a consequence, the evidence that the properties of multiple populations do not depend on stellar mass is a constraint for the formation scenarios.
- Hertzsprung-Russell and colour-magnitude diagrams
- globular clusters: individual: NGC 6752
- stars: Population II
- techniques: photometric
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science