Evidence of Early-stage Tidal Structures of Open Clusters Revealed by Kinematics with Gaia EDR3

TL;DR

This study uses Gaia EDR3 data to identify early-stage tidal disruption in open clusters, revealing that even clusters with a large bound fraction show signs of initial tidal tail formation.

Contribution

It provides the first evidence of early tidal disruption in open clusters other than Blanco 1, linking spatial elongation with kinematic tails.

Findings

Blanco 1 has well-developed tidal tails.

Pleiades and NGC 2516 show early signs of tidal disruption.

A correlation exists between spatial elongation and kinematic tails.

Abstract

Blanco 1, a 100Myr open cluster in the solar neighborhood, is well known for its two 50pc-long tidal tails. Taking Blanco 1 as a reference, we find evidence of early-stage tidal disruption in two other open clusters of ~120Myr: the Pleiades and NGC 2516, via Gaia EDR3 data. These two clusters have a total mass of 2-6 times that of Blanco 1. Despite having a similar age as Blanco 1, the Pleiades and NGC 2516 have a larger fraction of their members bound: 86% of their mass is inside the tidal radius, versus 63% for Blanco 1. However, a correlation between Blanco 1's 50pc-long tidal tails and the "kinematic tails" in velocity space is also found for the Pleiades and NGC 2516. This evidence supports the idea that the modest elongation seen in the spatial distribution for the Pleiades and NGC 2516 is a result of early-stage tidal disruption.