Disintegration of the Aged Open Cluster Berkeley 17

TL;DR

This study analyzes the shape and stellar population of Berkeley 17, the oldest known open cluster, revealing its core-tail structure, mass segregation, and clarifying the nature of blue straggler candidates.

Contribution

It provides a detailed morphological and stellar population analysis of Berkeley 17, confirming its core-tail shape and addressing the blue straggler contamination issue.

Findings

Confirmed core-tail and antitail structure of Berkeley 17

Detected mass segregation with low-mass stars in tails

Clarified that many blue straggler candidates are likely field stars

Abstract

We present the analysis of the morphological shape of Berkeley 17, the oldest known open cluster (~10 Gyr), using a probabilistic star counting of Pan-STARRS point sources, and confirm its core-tail shape, plus an antitail, previously detected with the 2MASS data. The stellar population, as diagnosed by the color-magnitude diagram and theoretical isochrones, shows many massive members in the cluster core, whereas there is a paucity of such members in both tails. This manifests mass segregation in this aged star cluster with the low-mass members being stripped away from the system. It has been claimed that Berkeley 17 is associated with an excessive number of blue straggler candidates. Comparison of nearby reference fields indicates that about half of these may be field contamination.