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

TL;DR

This study uses deep imaging and proper motion analysis to examine the white dwarf cooling sequence in M37, providing insights into the cluster's extended main sequence turn-off and ruling out age spread as its cause.

Contribution

It offers the first detailed white dwarf cooling sequence for M37, enabling comparison with models to understand the extended turn-off phenomenon.

Findings

White dwarf cooling sequence reaches the end at g ~ 23.5

Proper motions effectively separate cluster members from field stars

Age-spread scenario is excluded as the main cause of the extended turnoff

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 magnitudes 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). The here-derived atlas and calibrated catalogue of the sources in the field of view is publicly released as supplementary on-line 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 turnoff seen in the cluster colour-magnitude-diagram.