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A Double Main Sequence in the Globular Cluster NGC 6397

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abstract

High-precision multi-band HST photometry reveals that the main sequence (MS) of the globular cluster NGC 6397 splits into two components, containing ~30% and ~70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (i) a primordial population that has a composition similar to field stars, and containing ~30% of the stars, and (ii) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance (Delta Y~0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m_F336W. Theoretical isochrones indicate that this could be due to NH depletion.

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2026 1

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  • New Way to Date Globular Clusters: Brown Dwarf Cooling Sequences astro-ph.SR · 2026-03-08 · unverdicted · none · ref 101 · internal anchor

    A new histogram-free likelihood method applied to simulated JWST observations of brown dwarfs shows that globular cluster ages can be determined with formal errors under 0.2 Gyr.