Exploring Multiple Stellar Populations in Globular Clusters with Euclid: A Theoretical Overview and Insights from NGC 6397

TL;DR

This paper demonstrates that Euclid photometry can effectively distinguish multiple stellar populations in globular clusters, particularly among M-dwarfs, through theoretical modeling and analysis of NGC 6397, revealing population fractions and chemical differences.

Contribution

It provides the first comprehensive theoretical and observational analysis of multiple populations among M-dwarfs in a globular cluster using Euclid data, highlighting its potential as a powerful tool.

Findings

1P stars constitute about 30% of M-dwarfs in NGC 6397.

The fraction of 1P stars remains consistent across stellar masses and the entire field.

2P stars show an [O/Fe] depletion of about 0.3 dex.

Abstract

We investigate the behavior of multiple stellar populations in globular clusters (GCs) using photometric diagrams constructed with Euclid photometry. By employing synthetic spectra and isochrones that incorporate the chemical differences between first-population (1P) stars, resembling field stars, and second-population (2P) stars, enriched in helium and nitrogen but depleted in carbon and oxygen, we identify, from a theoretical perspective, the color-magnitude diagrams and the chromosome maps most effective at distinguishing these populations within GCs. Euclid photometry proves to be a powerful tool for identifying multiple populations among M-dwarfs, as 1P and 2P stars form distinct sequences in well-chosen photometric diagrams, driven by differences in the strength of oxygen-based molecular features, such as water vapor. To validate our theoretical findings, we analyzed Euclid photometry and astrometry of the GC NGC 6397, complemented by photometric and astrometric data from the Hubble Space Telescope and James Webb Space Telescope, enabling a comprehensive study of its stellar populations across a wide field of view. We find that the 1P constitutes about 30% of the M-dwarfs in NGC 6397, with the fraction of 1P stars remaining consistent across different stellar masses and throughout the entire field of view. 2P stars exhibit an [O/Fe] depletion of about 0.3 dex relative to 1P stars, and both populations display isotropic proper motions. This study represents the first comprehensive analysis of multiple populations among M-dwarfs across a wide field of view, demonstrating that Euclid photometry is a powerful instrument for investigating multiple populations in GCs.