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

Uncovering the properties of the nearby open cluster NGC 2682.


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 a fascinating dynamical history.

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

Based on new information from ESA‘s Gaia satellite, astronomers have offered detailed insights into the 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 the 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 about 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 to constrain its dynamic evolution.

Usually, most open clusters dissolve at the age of around 1 billion years, but the NGC 2682 survived until now. It means the cluster must have been much more massive in the past and 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 as 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. Astronomers say 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.

Journal Reference

  1. R. Carrera, M. Pasquato, A. Vallenari, L. Balaguer-Núñez, T. Cantat-Gaudin, M. Mapelli, A. Bragaglia, D. Bossini, C. Jordi, D. Galadí-Enríquez, E. Solano – The extended halo of NGC 2682 (M 67) from Gaia DR2. Astronomy & Astrophysics DOI: 10.1051/0004-6361/201935599
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