JWST imaging of the closest globular clusters—I. Possible infrared excess among white dwarfs in NGC 6397

Abstract

We present James Webb Space Telescope observations of the globular cluster NGC 6397 and use them to extend to infrared wavelengths the characterization of the cluster's entire white dwarf (WD) cooling sequence (CS). The data allows us to probe fundamental astrophysical WD properties and to search for evidence in their colors for (or against) the existence of ancient planetary systems. The existing archival Hubble Space Telescope imaging data obtained (Formula presented.) years ago reach ultra-deep optical magnitudes ((Formula presented.)) and allow us to derive a near-perfect separation between field and cluster members. We detect an apparent split in the lower part of the WD CS of NGC 6397. The red part of the WD CS, containing about 25% of the total, exhibits significant IR-excess of up to (Formula presented.) mag. These infrared excesses require both theoretical and observational follow-ups to confirm their veracity and to ascertain their true nature.