Exploring the origin of the extended main-sequence turn-off in M37 through the white dwarf cooling sequence

Abstract

ABSTRACT We use new observations from the Canada–France–Hawaii Telescope to study the white dwarf cooling sequence of the open cluster M37, a cluster that displays an extended main-sequence turn-off and, according to a recent photometric analysis, also a spread of initial chemical composition. By taking advantage of a first epoch collected in 1999 with the same telescope, we have been able to calculate proper motions for sources as faint as g ∼ 26 (about ∼ 6 mag fainter than the Gaia limit), allowing us to separate cluster members from field stars. This has enabled us to isolate a sample of the white dwarf population of M37, reaching the end of the cooling sequence (at g ∼ 23.5). Here, the derived atlas and calibrated catalogue of the sources in the field of view is publicly released as supplementary online material. Finally, we present an exhaustive comparison of the white dwarf luminosity function with theoretical models, which has allowed us to exclude the age-spread scenario as the main responsible for the extended turn-off seen in the cluster colour–magnitude diagram.