Search for blue straggler stars in open clusters from the VVV survey (preliminary result)

Abstract

Blue straggler stars (BSS) are a group of stars that are found within some stellar clusters through their color-magnitude diagrams (CMDs). The BSS are located on the upper-part of the CMD’s tum-off (TO) point along the zero-age main sequence (ZAMS) line. BSS are commonly found within intermediate-age to old stellar clusters, typically 108 years. Based on the catalogue of BSS in open clusters (OCs), the OCs toward the Galactic Center (GC) that host BSS are less than the ones toward the anti-center. Using the VVV survey data in near-infrared, we plan to investigate the presence of BSS in OCs toward the GC. To reach our objectives, we generally divide the works into: (1) determine cluster membership probability, (2) fit the decontaminated CMDs with its respectable isochrones, (3) detect any stars that fall into BSS area in CMD and recheck their position in spatial diagram. Out of the 4 OCs we planned to investigate, only 1 OC had been analyzed up to its membership probability; NGC 5999. However, we found 1541 stars as the most probable members, exceeded way too many compared to the literature. We still need to refine our method in the future work to clean more field stars.