Radial velocities and metallicities of red giant stars in the old open cluster NGC 7762

TL;DR

This study provides the first metallicity and radial velocity measurements for stars in the old open cluster NGC 7762, revealing it to be a solar-metallicity cluster approximately 2.5 billion years old, similar to Ruprecht 147.

Contribution

First metallicity and radial velocity measurements for NGC 7762, establishing its properties and comparison with similar nearby clusters.

Findings

NGC 7762 has solar metallicity ([Fe/H]=0.04±0.12).

The cluster is approximately 2.5 Gyr old.

Located at about 900 pc from the Sun, larger than previous estimates.

Abstract

We present and discuss radial velocity and the very first metallicity measurements for nine evolved stars in the poorly known old open cluster NGC 7762. We isolated eight radial velocity cluster members and one interloper. Radial velocities are in good agreement with previous studies. NGC 7762 turns out to be of solar metallicity within the uncertainties ([Fe/H]=0.04$\pm$0.12). For this metallicity, the cluster age is 2.5$\pm$0.2 Gyr, and falls in a age range where only a few old open clusters are known. With respect to previous studies, we find a larger distance, implying the cluster to be located at 900$^{+70}_{-50}$ pc from the Sun. For most of the elements we measure solar-scaled abundance ratios. We searched the literature for open clusters of similar age in the solar vicinity and found that NGC 7762 can be considered a twin of Ruprecht 147, a similar age cluster located at only 300 pc from the Sun. In fact, beside age, also metallicity and abundance ratios are very close to Ruprecht 147 values within the observational uncertainties.