NGC 6397 WFC/ACS and NIR/WFC3 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 have identified, from a theoretical perspective, the color-magnitude diagrams and the chromosome maps most effective at distinguishing these populations within GCs.

Euclid photometry has proven 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 Telescopeand James Webb Space Telescope, enabling a comprehensive study of its stellar populations across a wide field of view (FoV).