On the extended stellar structure around NGC 288

TL;DR

This study reveals an extended, clumpy stellar structure around NGC 288 up to 3.5 times its tidal radius, suggesting limited tidal tail formation and highlighting the need for further external region studies of globular clusters.

Contribution

First detailed analysis of NGC 288's external stellar structure using Pan-STARRS data, challenging previous tidal tail hypotheses and emphasizing the importance of external region studies.

Findings

Extended stellar structure up to 3.5 times the tidal radius.

Limited evidence for long tidal tails around NGC 288.

Interaction with the Milky Way's tidal field appears inefficient.

Abstract

We report on observational evidence of an extra-tidal clumpy structure around NGC 288 from an homogeneous coverage of a large area with the Pan-STARRS PS1 database. The extra-tidal star population has been disentangled from that of the Milky Way field by using a cleaning technique that successfully reproduced the stellar density, luminosity function and colour distributions of MW field stars. We have produced the cluster stellar density radial profile and a stellar density map from independent approaches, from which we found results in excellent agreement : the feature extends up to 3.5 times the cluster tidal radius. Previous works based on shallower photometric data sets have speculated on the existence of several long tidal tails, similar to that found in Pal 5. The present outcome shows that NGC 288 could hardly have such tails, but favours the notion that interactions with the MW tidal field has been a relatively inefficient process for stripping stars off the cluster. These results point to the need of a renewed overall study of the external regions of Galactic globular clusters (GGCs) in order to reliably characterise them. Hence, it will be possible to investigate whether there is any connection between detected tidal tails, extra-tidal stellar populations, extent diffuse halo-like structures with the GGCs' dynamical histories in the Galaxy.