Euclid: The convective-transition gap of 47 Tuc

We report the first detection of the 'convective-transition gap' (also known as the 'M-dwarf gap') in the globular cluster 47 Tuc (NGC 104). This feature, linked to a change in the physical properties of late-type dwarfs, has remained elusive, with only two detections so far. Leveraging the large number of stars, high resolution, and photometric precision enabled by Euclid, we detected a statistically significant, sharp discontinuity in the main-sequence luminosity function of 47 Tuc at I-E approximate to 22.9, which we identify as the convective-transition gap. A comparison of the observed properties of the gap in 47 Tuc with theoretical models shows how the gap can be a powerful diagnostic for probing the internal chemical structure of globular clusters and their multiple stellar populations. Following its initial discovery in the metal-poor cluster NGC 6397, the identification of a convective gap in the metal-rich 47 Tuc suggests that this feature is more general than previously thought. These results demonstrate that Euclid can be transformative well beyond cosmology, with impacts across multiple areas of astrophysics, including resolved stellar populations.