Extended Tidal Tails of IC 4756 detected by {\it Gaia} EDR3

TL;DR

This study discovers extended tidal tails around the 1 Gyr-old open cluster IC 4756 using Gaia EDR3 data, revealing detailed spatial and kinematic structures, mass segregation, and precise cluster parameters.

Contribution

First detection of extended tidal tails of IC 4756 using Gaia EDR3 data, with detailed analysis of cluster structure, kinematics, and stellar population.

Findings

Tidal tails extend up to 180 pc with an S-shape in spatial distribution.

Mass segregation is observed within the cluster.

Derived tidal radius is approximately 12.13 pc, and core radius is about 4.33 pc.

Abstract

We report the discovery of emerged tidal tails around open cluster IC 4756 ($\sim$ 1 Gyr) based on 644 members identified from {\it Gaia} EDR3. Three-dimensional spatial positions, two-dimensional tangential velocities $\left( x, y, z, \kappa \cdot \mu_{\alpha}^{*}/\varpi, \kappa \cdot \mu_{\delta}/\varpi \right)$ are utilized to determine the co-moving member candidates of IC 4756. Using a Bayesian method, we correct the distance for each cluster member. Two tidal tails extend up to 180 pc and display a S-shape in $X^{\prime}Y^{\prime}$ space (Cartesian coordinates focused on cluster center). A clean sequence of our members in Color-Absolute-Magnitude Diagram (CAMD) indicates the coeval population and matches perfectly with the PARSEC isochrone with age from Bossini et al. (2019). Mass segregation is detected in this cluster as well. Finally, we derive the tidal radius and core radius of IC 4756 about $12.13$ pc and $4.33 \pm 0.75$ pc, respectively.