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

Abstract

Blanco 1, a 100\u2009Myr open cluster in the solar neighborhood, is well known for its two 50\u2009pc long tidal tails. Taking Blanco 1 as a reference, we find evidence of early-stage tidal disruption in two other open clusters of ∼120\u2009Myr: the Pleiades and NGC\u20092516, via Gaia EDR3 data. These two clusters have a total mass of 2–6 times that of Blanco\u20091. Despite having a similar age as Blanco\u20091, the Pleiades and NGC\u20092516 have a larger fraction of their members bound: 86% of their mass is inside the tidal radius, versus 63% for Blanco\u20091. However, a correlation between Blanco\u20091 s 50\u2009pc long tidal tails and the “kinematic tails” in velocity space is also found for the Pleiades and NGC\u20092516. This evidence supports the idea that the modest elongation seen in the spatial distribution for the Pleiades and NGC\u20092516 is a result of early-stage tidal disruption.