The Rotation Period Distribution in the Young Open Cluster NGC 6709

TL;DR

This study measures the rotation periods of 45 stars in the young open cluster NGC 6709, providing new data to test models of stellar spin-down and comparing its rotation distribution to similar clusters.

Contribution

First measurement of rotation periods for 45 stars in NGC 6709, enabling comparison with other clusters and testing of stellar rotation models.

Findings

NGC 6709 shows a slow-rotating sequence similar to NGC 2516.

Presence of rapid rotators not yet on the slow sequence.

Rotation periods increase with redder star colors.

Abstract

Open clusters serve as a useful tool for calibrating models of the relationship between mass, rotation, and age for stars with an outer convection zone due to the homogeneity of the stars within the cluster. Cluster to cluster comparisons are essential to determine whether the universality of spin down relations holds. NGC 6709 is selected as a young open cluster for which no rotation periods of members have previously been obtained. This cluster is at a distance of over 1 kpc and has two red giant members. Isochrones place the age of the cluster at around 150 Myr, or approximately the same age as the Pleiades. Photometry is obtained over a multi-month observing season at the robotic observatory STELLA. After basic processing, PSF photometry was derived using Daophot II, and a suite of related software allowed us to create time series of relative magnitude changes for each star. Four time series analysis methods are then applied to these light curves to obtain rotation periods for members stars. We obtain for the first time rotation periods for 45 FGK cluster members of NGC 6709. We compare our rotation periods to Gaia EDR3 colors and find a slow-rotating sequence with increasing rotation periods towards redder stars and a smaller clump of rapid rotators that have not yet joined this sequence. NGC 6709 has rotation periods very similar to that of another Pleiades-age open cluster, NGC 2516.