JWST photometry and astrometry of 47 Tucanæ. Discontinuity in the stellar sequence at the star–brown dwarf transition
Creators
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1.
University of Ferrara
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2.
Osservatorio Astronomico di Padova
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3.
University of Notre Dame
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Indiana University Bloomington
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Astronomical Observatory of Rome
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6.
Agenzia Spaziale Italiana
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University of Padua
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University of California, San Diego
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9.
University of British Columbia
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Institute of Science and Technology Austria
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11.
California Institute of Technology
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12.
Space Telescope Science Institute
Abstract
Using JWST Near Infrared Camera (NIRCam) images of the globular cluster 47 Tucanæ (or NGC 104), taken at two epochs just 7 months apart, we derived proper-motion membership down to mF322W2 ∼ 27. We identified an intriguing feature at the very low-mass end of the main sequence, around ∼0.08 M⋅, at magnitudes mF322W2 ∼ 24 and mF150W2 ∼ 25. This feature, dubbed ‘kink’, is characterized by a prominent discontinuity in the slope of the main sequence. A similar discontinuity is seen in theoretical isochrones with oxygen-poor chemistries, related to the rapid onset of CH4 absorption. We therefore hypothesize that the cluster hosts disproportionately more oxygen-poor stars near the bottom of the main sequence compared to the upper main sequence and the red giant branch. Our results show no strong or conclusive evidence of a rise in the brown dwarf luminosity function at faint magnitudes, in contrast to previous findings likely affected by faint red background galaxies. In our analysis, we accounted for this contamination by using proper motion membership.
Copyright and License
© The Authors 2025.
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.
Acknowledgement
We dedicate this paper to the memory of our colleague Prof. Harvey Richer (⋆ April 1944 —† 13 November 2023), a highly accomplished astronomer and expert in stellar populations and in particular within globular clusters, who passed away during this project. Harvey grew up in Montreal and was at least the second star man to graduate from his high school, having been preceded by William Shatner by more than a decade. He worked at the University of British Columbia for most of his career, and his focus was the late stages of stellar evolution, in particular carbon stars and white dwarfs. We thank the referee for his valuable suggestions and comments, which helped improve the paper, as well as for his prompt revision.
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2501.04446 (arXiv)
Dates
- Accepted
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2025-01-07Accepted
- Available
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2025-02-04Published online