Exploring Unusual Stellar Chemistry with Unconventional Observables
Few environments in the Galaxy defy the core expectations of chemical evolution as strongly as globular clusters. Most elements of the periodic table are forged in explosive astrophysical events. Yet despite being insufficiently massive to retain supernova ejecta, globular clusters show clear signatures of chemical evolution. While most metal-poor stellar populations are significantly α-enhanced, globular clusters frequently host stars with strongly depleted oxygen and magnesium abundances. This anomalous chemistry is not observed anywhere else in the Galaxy and is yet to be conclusively linked to an established enrichment mechanism. Even the timescale on which these abundance patterns emerge remains largely unconstrained.
While the chemistry of globular clusters has traditionally been studied through high-resolution spectroscopy of their brightest members, several unconventional observables now offer new ways to probe this persistent puzzle. I will highlight three examples: (1) r-process dispersion inferred from low-resolution spectroscopy, (2) the transition from oxygen- to carbon-dominated chemistry in the brown dwarf regime revealed by JWST photometry, and (3) direct insights into stellar structure on the lower main sequence from ultrawide-field observations with Euclid space telescope.
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