Morphology of Open Clusters NGC 1857 and Czernik 20 using Clustering Algorithms

TL;DR

This study applies clustering algorithms, including a novel use of DBSCAN, to analyze the morphology and membership of open clusters Czernik 20 and NGC 1857 using infrared survey data, providing new insights into their structure and properties.

Contribution

The paper introduces the first application of DBSCAN for open cluster morphology analysis and combines it with statistical membership and isochrone fitting for detailed cluster characterization.

Findings

Identified dense regions within clusters using DBSCAN.

Derived reliable distance and reddening parameters through CMD analysis.

Discovered a new over-density consistent with a star cluster.

Abstract

The morphology and cluster membership of the Galactic open clusters - Czernik 20 and NGC 1857 were analyzed using two different clustering algorithms. We present the maiden use of density-based spatial clustering of applications with noise (DBSCAN) to determine open cluster morphology from spatial distribution. The region of analysis has also been spatially classified using a statistical membership determination algorithm. We utilized near infrared (NIR) data for a suitably large region around the clusters from the United Kingdom Infrared Deep Sky Survey Galactic Plane Survey star catalogue database, and also from the Two Micron All Sky Survey star catalogue database. The densest regions of the cluster morphologies (1 for Czernik 20 and 2 for NGC 1857) thus identified were analyzed with a K-band extinction map and color-magnitude diagrams (CMDs). To address significant discrepancy in known distance and reddening parameters, we carried out field decontamination of these CMDs and subsequent isochrone fitting of the cleaned CMDs to obtain reliable distance and reddening parameters for the clusters (Czernik 20: D = 2900 pc; E(J-K) = 0.33; NGC 1857: D = 2400 pc; E(J-K) = 0.18-0.19). The isochrones were also used to convert the luminosity functions for the densest regions of Czernik 20 and NGC 1857 into mass function, to derive their slopes. Additionally, a previously unknown over-density consistent with that of a star cluster is identified in the region of analysis.