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Arxiv: JWST imaging of the closest globular clusters -- IV. Chemistry, luminosity, and mass functions of the lowest-mass members in the NIRISS parallel fields Published: 9/10/2024 9:00:01 PM Updated: 9/10/2024 9:00:01 PM

Paper abstract: We present observations of the two closest globular clusters, NGC 6121 andNGC 6397, taken with the NIRISS detector of JWST. The combination of our newJWST data with archival Hubble Space Telescope (HST) images allows us tocompute proper motions, disentangle cluster members from field objects, andprobe the main sequence (MS) of the clusters down to <0.1 M_\odot as well asthe brighter part of the white-dwarf sequence. We show that theoreticalisochrones fall short in modeling the low-mass MS and discuss possibleexplanations for the observed discrepancies. Our analysis suggests that thelowest-mass members of both clusters are significantly more metal-rich andoxygen-poor than their higher-mass counterparts. It is unclear whether thedifference is caused by a genuine mass-dependent chemical heterogeneity,low-temperature atmospheric processes altering the observed abundances, orsystematic shortcomings in the models. We computed the present-day localluminosity and mass functions of the two clusters; our data reveal a strongflattening of the mass function indicative of a significant preferential lossof low-mass stars in agreement with previous dynamical models for these twoclusters. We have made our NIRISS astro-photometric catalogs and stacked imagespublicly available to the community.