NGC 2158

Once thought to be a globular cluster, it is now known to be a metal-poor open cluster that is a member of the old thin disk population. It was first classed as such by Trumpler but later Shapley would classify it as an open cluster due to its diffuse core. NGC 2158 has been studied numerous times. A study from Arp & Cuffey (1962) was the first study of NGC 2158 obtaining photographic photometry for about 900 stars and determine the cluster to be an intermediate between regular star clusters and globular clusters. Later, the photometry of more than 2000 stars would be obtained by Karchenko, Andruk & Schilbach (1997). == Properties ==

NGC 2158 has unusual properties for an open cluster (OC). Its rich stellar content (only with suitable equipment can spaces between the stars be seen) and brightness initially makes it appear as a globular cluster (GC). It also has a red giant population similar to GCs. However it is not and is rather an intermediate object between globular clusters and regular star clusters. The cluster has anomalously low amount of metals making it metal-poor. It has been estimated that NGC 2158 is around 2 billion years old. This would make the cluster of intermediate-age. == Contents ==

NGC 2158 is a populous cluster with many low to intermediate mass stars. NGC 2158 has three mass regimes: high mass stars, low mass stars and very low mass stars. Data used from the third edition of the Gaia Data Release (DR3) revealed that there are 3067 ±69.84 stars totaling to a mass of 3216.4 ±59.50 solar masses. There is a red giant population. It also contains a cataclysmic variable (CV) star (the fourth known to exist in a open cluster) and five Delta Scuti variables (δ Scuti). Due to the distance of NGC 2158, most binary systems that survived inside the dense environment are unable to be resolved. Instead, these systems appear as point-like sources with the exception of wide binary systems which can be resolved as two distinct sources. ==Additional images==