Multiple stellar populations in globular clusters with JWST: an NIRCam view of 47 Tucanae

We use images collected with the near-infrared camera (NIRCam) onboard the JWST and with the Hubble Space Telescope (HST) to investigate multiple populations at the bottom of the main sequence (MS) of 47 Tucanae. The m_F115W versus m_F115W - m_F322W2 colour-magnitude diagram (CMD) from NIRCam shows that, below the knee, the MS stars span a wide colour range, where the majority of M-dwarfs exhibit blue colours, and a tail of stars are distributed towards the red. A similar pattern is observed from the m_F160W versus m_F110W - m_F160W CMD from HST, and multiple populations of M-dwarfs are also visible in the optical m_F606W versus m_F606W - m_F814W CMD. The NIRCam CMD shows a narrow sequence of faint MS stars with masses smaller than $0.1\, \mathcal {M}_{\odot }$. We introduce a chromosome map of M-dwarfs that reveals an extended first population and three main groups of second-population stars. By combining isochrones and synthetic spectra with appropriate chemical composition, we simulate colours and magnitudes of different stellar populations in the NIRCam filters (at metallicities [Fe/H] = -1.5 and [Fe/H] = -0.75) and identify the photometric bands that provide the most efficient diagrams to investigate the multiple populations in globular clusters. Models are compared with the observed CMDs of 47 Tucanae to constrain M-dwarfs' chemical composition. Our analysis suggests that the oxygen range needed to reproduce the colours of first- and second-population M-dwarfs is similar to that inferred from spectroscopy of red giants, constraining the proposal that the chemical variations are due to mass transfer phenomena in proto-clusters.