Tidal tails of nearby open clusters I. Mapping with Gaia DR3

Abstract

Context: Tidal tails of open clusters are the result of stellar evaporation from the cluster through the Galactic potential and internal dynamics. With the recent availability of high-precision data, tidal tails are being detected for most of the nearby open clusters. Aims: We identify the tidal tail members for all open clusters within a distance of 400 pc that are older than 100 Myr and have $>$100 members. To do this, we use model-independent methods. Methods: We used the convergent-point (CP) method to identify the co-moving stars near the open clusters using Gaia DR3 data. A new method called the self-compact convergent-point (SCCP) method was proposed and applied to some of the clusters. It performed better overall in tracing the tails. We also analysed the colour-magnitude diagrams and orbital energy to diagnose possible contamination. Results: Nineteen out of 21 clusters have tidal tails. Five of them were discovered for the first time through this work. The typical span of the tidal tails is 20--200 pc, and 30--700 member stars lie in the region inside the tidal radius and the tidal tails. Four out of 19 tidal tails are tilted away from direction of the Galactic centre. This contradicts the known theory of the tidal-tail formation. The luminosity functions of the tails and clusters are consistent with each other and with the canonical stellar interstellar mass function, but systematically higher radial velocities for the trailing tail than for the leading tail were observed for the first time. Conclusions: The CP method is useful for detecting tidal tails on a scale of approx. 100 pc for clusters closer than 400 pc. A further analysis of theoretical N-body models is required to understand the incompleteness and biases in the current sample of tidal tails.