The Contributions of Interactive Binary Stars to Double Main Sequence Turn-Offs and Dual Red Clump of Intermediate-Age Star Clusters

TL;DR

This paper investigates how binary star interactions and mergers can explain the observed double main-sequence turn-offs and dual red clumps in intermediate-age star clusters, challenging the need for multiple stellar populations.

Contribution

It demonstrates through stellar population-synthesis modeling that binary interactions can produce features previously attributed to multiple populations in clusters.

Findings

Binary interactions can reproduce dual red clumps in models.

Extended MSTOs can result from binary interactions, not multiple populations.

Most of the main sequence and giant branches are unaffected by binary interactions.

Abstract

Double or extended main-sequence turn-offs (DMSTOs) and dual red clump (RC) were observed in intermediate-age clusters, such as in NGC 1846 and 419. the DMSTOs are interpreted as that the cluster has two distinct stellar popula- tions with differences in age of about 200-300 Myr but with the same metallicity. The dual RC is interpreted as a result of a prolonged star formation. Using a stellar population-synthesis method, we calculated the evolutions of binary-star stellar population (BSP). We found that binary interactions and merging can reproduce the dual RC in the color-magnitude diagrams of an intermediate-age cluster, whereas in actuality only a single population exists. Moreover, the binary interactions can lead to an extended MSTO rather than DMSTOs. However, the rest of main sequence, subgiant branch and first giant branch are hardly spread by the binary interactions. Part of the observed dual RC and extended MSTO may be the results of binary interactions and merger.