Open cluster NGC 2682 at least two times larger than previously thought

Uncovering the properties of the nearby open cluster NGC 2682.

NGC 2682. Credit: 2MASS/UMass/IPAC-Caltech/NASA/NSF
NGC 2682. Credit: 2MASS/UMass/IPAC-Caltech/NASA/NSF

NGC 2682 is a nearby open cluster, approximately 3.5 Gyr old. Dynamically, most open clusters should dissolve on shorter timescales, of ~ 1 Gyr. Having survived until now, NGC 2682 was likely much more massive in the past and is bound to have an interesting dynamical history.

Notably, its age and initial chemical composition is similar to that of the sun. Thus, astronomers even considered that the sun might actually have originated from NGC 2682.

Based on new information from ESA‘s Gaia satellite, astronomers have offered detail insights into properties of the nearby open cluster NGC 2682. They revealed that its size is, at least two times greater than recently believed.

Almost a year ago, data from Gaia satellite (known as Data Release 2, or DR2) provided high-precision measurements, including positions in the sky, parallaxes and proper motions for more than 1 billion sources in the Milky Way.

Undoubtedly, DR2 can potentially uncover more information into the nature of NGC 2682 as the information could be a valuable tool to investigate extra-tidal regions of several open clusters in the solar neighborhood. Thus, ESA scientists used DR2 and investigated the spatial distribution of this cluster of stars in order to constrain its dynamical evolution.

Usually, most of the open clusters dissolve at an age of around 1 billion years, but the NGC 2682 survived until now. It means, the cluster must be much more massive in the past and also had an interesting dynamical history.

Using Gaia DR2, astronomers were able to identify NGC 2682 members up to a distance of about 150 pc (10 degrees). They then applied two methods: Clusterix and UPMASK to this end.

Scientists noted, “We estimate distances to obtain three-dimensional stellar positions using a Bayesian approach to parallax inversion, with an appropriate prior for star clusters.”

The outcomes suggest that NGC 2682 is at least twice as large than previously thought. Moreover, astronomers also found that this cluster extends up to approximately 160 light years.

Furthermore, the study confirmed that NGC 2682 is mass-segregated with the most massive objects concentrated in the central regions. However, there are also stars outside the tidal radius of this cluster. According to astronomers, these extra-tidal stars in NGC 2682 may originate from external perturbations such as disk shocking or dynamical evaporation from two-body relaxation. They also plan more studies of the cluster to test these scenarios.