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Abstract Stars in an open cluster are assumed to have formed from a broadly homogeneous distribution of gas, implying that they should be chemically homogeneous. Quantifying the level to which open clusters are chemically homogeneous can therefore tell us about interstellar medium pollution and gas mixing in progenitor molecular clouds. Using Sloan Digital Sky Survey (SDSS)-V Milky Way Mapper and SDSS-IV Apache Point Observatory Galaxy Evolution Experiment DR17 abundances, we test this assumption by quantifying intrinsic chemical scatter in up to 20 different chemical abundances across 26 Milky Way open clusters. We find that we can place 3σupper limits on open cluster homogeneity within 0.02 dex or less in the majority of elements, while for neutron capture elements, as well as those elements having weak lines, we place limits on their homogeneity within 0.2 dex. Finally, we find that giant stars in open clusters are ∼0.01 dex more homogeneous than a matched sample of field stars. 

Accurate stellar ages are crucial for galactic archeology, but cannot be measured directly. Evolved red giant stars offer a solution, since their lifetimes can be inferred from their masses. Mass measurements often rely on mass proxies, such as the surface carbon-to-nitrogen ratio ([C/N]) after the first dredge-up. But this relationship is not consistent for all stars. Understanding the systematics behind these [C/N] outliers is essential for improving mass and subsequent age measurements. We analyze additional elemental abundances, such as those of s-process elements, that may indicate binary interactions. We find significant differences between typical and outlier stars, suggesting atypical or binary evolution histories for outlier stars. By accounting for such complexities in this method, more accurate stellar ages and a clearer picture of the Milky Way’s formation and evolution will be understood.