# The HST Large Programme on NGC6752. II. Multiple populations at the bottom of the main sequence probed in NIR

## TL;DR

This study uses deep near-infrared photometry from the Hubble Space Telescope to identify and analyze multiple stellar populations among low-mass M-dwarfs in the globular cluster NGC6752, revealing that multiple populations are common across different stellar masses.

## Contribution

First detection of multiple populations among M-dwarfs in NGC6752 using NIR photometry, extending the understanding of multiple populations to lower stellar masses.

## Key findings

- Three distinct sequences of M-dwarfs identified in NGC6752.
- Multiple populations show different oxygen abundances consistent with RGB star measurements.
- The properties of multiple populations are similar across different stellar masses.

## Abstract

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 solar masses. Here we exploit deep near-infrared (NIR) photometry from the Hubble Space Telescope to investigate multiple populations among M-dwarfs in the GC NGC6752. We discovered that the three main populations (A, B and C), previously observed in the brightest part of the color-magnitude diagram, define three distinct sequences that run from the main-sequence (MS) knee towards the bottom of the MS (~0.15 solar masses). These results, together with similar findings on NGC2808, M4, and omega Centauri, demonstrate that multiple sequences of M-dwarfs are common features of the color-magnitude diagrams of GCs. The three sequences of low-mass stars in NGC6752 are consistent with stellar populations with different oxygen abundances. The range of [O/Fe] needed to reproduce the NIR CMD of NGC6752 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 solar masses. As a consequence, the evidence that the properties of multiple populations do not depend on stellar mass is a constraint for the formation scenarios.