  Despite their shared origin, members of globular clusters display
star-to-star variations in composition. The observed pattern of element
abundances is unique to these stellar environments, and cannot be fully
explained by any proposed mechanism. It remains unclear whether stars form with
chemical heterogeneity, or inherit it from interactions with other members.
These scenarios may be differentiated by the dependence of chemical spread on
stellar mass; however, obtaining a sufficiently large mass baseline requires
abundance measurements on the lower main sequence that is too faint for
spectroscopy even in the nearest globular clusters. We developed a stellar
modelling method to obtain precise chemical abundances for stars near the end
of the main sequence from multiband photometry, and applied it to the globular
cluster 47 Tucanae. The computational efficiency is attained by matching
chemical elements to the model components that are most sensitive to their
abundance. We determined [O/Fe] for ~5000 members below the main sequence knee
at the level of accuracy, comparable to the spectroscopic measurements of
evolved members in literature. The inferred distribution disfavors stellar
interactions as the origin of chemical spread; however, an accurate theory of
accretion is required to draw a more definitive conclusion. We anticipate that
future observations of 47 Tucanae with JWST will extend the mass baseline of
our analysis into the substellar regime. Therefore, we present predicted
color-magnitude diagrams and mass-magnitude relations for the brown dwarf
members of 47 Tucanae.
