A JWST project on 47 Tucanae. Overview, photometry and early spectroscopic results of M dwarfs, and observation of brown dwarfs

TL;DR

This study demonstrates JWST's effectiveness in detecting and analyzing multiple stellar populations in the low-mass regime of 47 Tucanae, including M dwarfs and brown dwarfs, revealing substructures and consistent population fractions across masses.

Contribution

First comprehensive JWST analysis of multiple populations in very low mass stars and brown dwarfs within a globular cluster, including spectroscopic and photometric results.

Findings

Detection of substructures in ultracool stars' CMD.

Identification of a luminosity gap and minimum related to the H-burning limit.

Confirmation of multiple populations across a wide stellar mass range.

Abstract

The James Webb Space Telescope (JWST) observations have been demonstrated to be efficient in detecting globular clusters' (GCs) multiple stellar populations in the low mass regime of M dwarfs. We present an overview, and first results, of different projects that can be explored by using the JWST observations gathered under the GO2560 for 47 Tucanae, a first program entirely devoted to the investigation of multiple populations in very low mass stars, which includes spectroscopic data for the faintest GC stars for which spectra are available. Our color-magnitude diagram (CMD) shows some substructures for ultracool stars, including gaps and breaks in slope. In particular, we observe both a gap and a minimum in the F322W2 luminosity function less than one magnitude apart, and discuss which one could be associated with the H-burning limit. We detect stars fainter than this minimum, very likely the brown dwarfs. We corroborate the ubiquity of the multiple populations across different masses, from ~0.1 solar masses up to red giants (~0.8 solar masses). The oxygen range inferred from the M dwarfs, both from the CMD and from the spectra of two M dwarfs associated with different populations, is similar to that observed in giants. We have not detected any difference between the fractions of stars in distinct populations across stellar masses >~0.1 solar masses. This work demonstrates the JWST's capability in uncovering multiple populations within M dwarfs and illustrates the possibility to analyse very low-mass stars in GCs approaching the H-burning limit and the brown-dwarf sequence.