Issue |
A&A
Volume 679, November 2023
|
|
---|---|---|
Article Number | L13 | |
Number of page(s) | 7 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202347961 | |
Published online | 28 November 2023 |
Letter to the Editor
JWST uncovers helium and water abundance variations in the bulge globular cluster NGC 6440
1
Dipartimento di Fisica e Astronomia “Augusto Righi”, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
e-mail: mario.cadelano@unibo.it
2
INAF-Osservatorio di Astrofisica e Scienze dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
3
Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
4
INAF – Osservatorio Astronomico d’Abruzzo, Via M. Maggini, 64100 Teramo, Italy
5
Max-Planck-Institut für Radioastronomie MPIfR, Auf dem Hügel 69, 53121 Bonn, Germany
6
Department of Physics, University of Alberta, Edmonton, AB T6G 2G7, Canada
7
NRAO, 520 Edgemont Road, Charlottesville, VA 22903, USA
Received:
14
September
2023
Accepted:
17
October
2023
We used ultra-deep observations obtained with the NIRCam aboard the James Webb Space Telescope to explore the stellar population of NGC 6440: a typical massive, obscured, and contaminated globular cluster formed and orbiting within the Galactic bulge. Leveraging the exceptional capabilities of this camera, we sampled the cluster down to about five magnitudes below the main sequence turn-off in the (mF115W, mF115W − mF200W) colour–magnitude diagram. After carefully accounting for differential extinction and contamination by field interlopers, we find that the main sequence splits into two branches, each above and below the characteristic knee. By comparing the morphology of the colour–magnitude diagram with a suitable set of isochrones, we argue that the upper main sequence bi-modality is likely due to the presence of a He-enriched stellar population with a helium spread of ΔY = 0.04. The lower main sequence bi-modality can be attributed to variations in the abundance of water (i.e., oxygen) with Δ[O/Fe] ∼ −0.4. This is the first evidence of both helium and oxygen abundance variations in a globular cluster purely based on JWST observations. These results open the window for future in-depth investigations of the multiple population phenomenon in clusters located in the Galactic bulge, which were previously unfeasible with near-UV observations, due to prohibitive reddening and crowding conditions.
Key words: globular clusters: general / globular clusters: individual: NGC 6440 / Galaxy: bulge / techniques: photometric / stars: chemically peculiar / infrared: stars
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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