AAOmega radial velocities rule out current membership of the planetary nebula NGC 2438 in the open cluster M46

TL;DR

This study uses new radial velocity data to conclusively determine that the planetary nebula NGC 2438 is not a member of the open cluster M46, resolving previous uncertainties.

Contribution

The paper provides the first comprehensive radial velocity measurements of stars in M46 and NGC 2438, conclusively ruling out their association based on velocity differences.

Findings

NGC 2438's velocity differs by about 30 km/s from M46.

The velocity dispersion of M46 is approximately 3.9 km/s.

The cluster's velocity dispersion may be influenced by binary stars.

Abstract

We present new radial velocity measurements of 586 stars in a one-degree field centered on the open cluster M46, and the planetary nebula NGC 2438 located within a nuclear radius of the cluster. The data are based on medium-resolution optical and near-infrared spectra taken with the AAOmega spectrograph on the Anglo-Australian Telescope. We find a velocity difference of about 30 km/s between the cluster and the nebula, thus removing all ambiguities about the cluster membership of the planetary nebula caused by contradicting results in the literature. The line-of-sight velocity dispersion of the cluster is 3.9+/-0.3 km/s, likely to be affected by a significant population of binary stars.