The relation of the Alpha Persei star cluster with the nearby stellar stream

TL;DR

This study uses Gaia DR2 data and DBSCAN clustering to distinguish the Alpha Persei star cluster from a nearby stellar stream, revealing their distinct properties, ages, and possible origins.

Contribution

It provides a detailed characterization of the Alpha Persei stream and its relation to the cluster, including age, distance, and stellar composition, using a novel application of clustering analysis.

Findings

The stream is significantly older (~5 Gyr) than the cluster.

The stream is located ~90 pc behind the cluster and has a thickness of ~180 pc.

The stream contains a notable population of white dwarf stars.

Abstract

A map of 100 degrees on a side extracted from Gaia DR2 and centred on Alpha Persei reveals two distinct structures | the Alpha Persei star cluster and a conspicuous stellar stream, as widely documented in recent literature. In this work we employ DBSCAN to assess individual stars' membership and attempt at separating stars belonging to the cluster and to the stream from the general field. In turn, we characterize the stream and investigate its relation with the cluster. The stream population turned out to be significantly older (5+/-1Gyr) than the cluster, and to be positioned ~90 pc away from the cluster, in its background. The stream exhibits a sizeable thickness of ~180 pc in the direction of the line of view. Finally, the stream harbours a prominent population of white dwarf stars. We estimated an upper limit of the stream mass of ~6000 solar masses?. The stream would therefore be the leftover of a relatively massive old cluster. The surface density map of the Alpha Persei evidences the presence of tidal tails. While it is tempting to ascribe them to the interaction with the disrupting old star cluster, we prefer to believe, conservatively, they are of Galactic origin.