A JWST Project on 47 Tucanae. Overview, Photometry, and Early Spectroscopic Results of M Dwarfs and Observations of Brown Dwarfs*

Abstract

James Webb Space Telescope (JWST) observations have been demonstrated to be efficient in detecting multiple stellar populations in globular clusters (GCs) 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 program GO2560 for 47 Tucanae, the 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 1 mag apart, and discuss which it could be associated with the H-burning limit. We detect stars fainter than this minimum, very likely brown dwarfs. We corroborate the ubiquity of the multiple populations across different masses, from ∼0.1 M ⊙ up to red giants (∼0.8 M ⊙). The oxygen range inferred for the M dwarfs, both from the CMD and from the spectra of two M dwarfs associated with different populations, is similar to that observed for giants. We have not detected any difference between the fractions of stars in distinct populations across stellar masses ≳ 0.1 M ⊙. This work demonstrates the JWST's capability in uncovering multiple populations within M dwarfs and illustrates the possibility to analyze very-low-mass stars in GCs approaching the H-burning limit and the brown-dwarf sequence.

A JWST Project on 47 Tucanae: NIRSpec Spectroscopy of Multiple Populations among M Dwarfs*

“…A visual comparison of the two spectra shown in Figure 1 (see also Figure 8 of Marino et al 2024 for another pair of stars) clearly reveals different absorption for stars belonging to distinct stellar populations. The position of these two stars on the cluster chromosome map (ChM; see Milone et al 2017a) shown in the right panel of Figure 1, suggests that #32620 is a 1P star, whereas #25862 is one of the most extremely polluted 2P stars, which we expect to be associated with the lowest oxygen abundance.…”

“…To simultaneously observe many targets, we employed the multiobject spectroscopy mode using the micro-shutter assembly (MSA) configuration. In parallel, NIRCam was observed in the two filters F115W and F322W2, those that most efficiently ensure the separation of multiple sequences among M dwarfs (Milone et al 2023;Marino et al 2024), again using H 2 O blanketing but this time in the F322W2 passband.…”

“…This time we did not experience any failure and obtained new images and spectra. While for the photometric analysis and the presentation of the first spectra we refer to Marino et al (2024), here we analyze the full spectroscopic data set.…”

“…The location of the NIRSpec and NIRCam parallel fields are shown in Marino et al (2024; see their Figure 1). Specifically, the NIRSpec field has pointed to the same field previously covered with HST, for which the filters F110W and F160W from GO11453 are available.…”

“…The first evidence of multiple stellar populations in very low-mass stars below the mainsequence knee has been reported for NGC 104 (47 Tucanae; Milone et al 2023), M 92 (Ziliotto et al 2023), and NGC 6440 (Cadelano et al 2023), using H 2 O blanketing (e.g., in the F150W, F200W, or F322W2 bands). Most recently, the CMD of 47 Tucanae from very deep JWST/NIRCam data has reached, for the first time, the H-burning limit and the more luminous brown dwarfs (Marino et al 2024).…”