Exploring the Chemistry and Mass Function of the Globular Cluster 47 Tucanae with New Theoretical Color-Magnitude Diagrams

TL;DR

This study introduces a new photometric method to determine chemical abundances in faint stars of 47 Tucanae, enabling insights into stellar formation and chemical variation across a broader mass range.

Contribution

The paper presents a novel stellar modeling technique using multiband photometry to measure chemical abundances in faint main sequence stars of 47 Tucanae.

Findings

Chemical spread likely not caused by stellar interactions

Achieved spectroscopic-like abundance accuracy for ~5000 stars

Predicted color-magnitude diagrams for brown dwarf members

Abstract

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.