Astronomy departmental seminar - Janez Kos (University of Ljubljana)


Tidal tails of open clusters

Tidal tails of open clusters have first been observed only in the recent couple of years. Like the tails of globular clusters and satellite galaxies, they can be used as important probes of gravitational fields, galactic evolution, disk kinematics, and stellar evolution. Recent progress has been possible with the arrival of Gaia data releases, so we can find tails of structures 1000 times smaller than globular clusters in the environment 1000 times denser than the halo. I will present a probabilistic method that does not directly rely on finding overdensities. We use simulations of cluster disintegration to define likelihoods for Gaia stars to be cluster members, and simulations of the Galactic stellar population to define membership probabilities. In an analysis of 500 clusters, we reliably find stars in tidal tails 1000 pc away from cluster cores. I will also discuss the need for precise radial velocities (not used in our method), obtaining more complete mass functions, and observed oddities that hint at numerous kinematical processes that shape the tidal tails.