A tale of caution: the tails of NGC 752 are much longer than claimed. Issue 3 (9th June 2022) - Boffin, Henri M J
ABSTRACT: Understanding the exact extent and content of tidal tails of open clusters provides useful clues on how field stars populate the Milky Way. We reanalyse, using Gaia EDR3 data, the tails around the open cluster NGC 752. Compared to previous analyses, we look at a much wider region around the cluster and use first the convergent point method, coupled with a clustering analysis using dbscan . We find that the cluster, located 433 pc away and well described by a Plummer profile, has very long and asymmetric tails, extending more than 260 pc on the sky (from tip to tip) – four times larger than previously thought – and contains twice as many stars. Numerical models computed with petar serve as a guide and confirm our analysis. The tails follow the predictions from the models, but the trailing tail appears slightly distorted, possibly indicating that the cluster had a complicated history of galactic encounters. Applying an alternative method to the newly developed compact convergent point method, we potentially trace the cluster's tidal tails to their full extent, covering several thousands of parsecs and more than 1000 stars. Our analysis therefore opens a new window on the study of open clusters, whose potential will be fully unleashed with future Gaia data releases.