Extended Tidal Tails of IC 4756 Detected by Gaia EDR3

We report the discovery of emerged tidal tails around open cluster IC 4756 (∼1 Gyr) based on 644 members identified from Gaia EDR3. Three-dimensional spatial positions and two-dimensional tangential velocities $(x,y,z,\kappa \cdot {\mu }_{\alpha }^{\ast }/\varpi ,\kappa \cdot {\mu }_{\delta }/\varpi )$ are utilized to determine the comoving 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 an S shape in the $X^{\prime }{Y}^{\prime }$ space (Cartesian coordinates focused on cluster center). A clean sequence of our members in the color–absolute–magnitude diagram indicates the coeval population and matches perfectly with the PARSEC isochrone with age from Bossini et al. 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 ± 0.75 pc, respectively.