Study Sheds Light on NGC 1851’s Variable Stars

Astronomers have recently conducted photometric observations of the young globular cluster known as NGC 1851. This new observational campaign offers deeper insights into the cluster's variable star population and confirms the membership of these stars. The results were published on August 20 on the pre-print server arXiv.

Studying variable stars can provide valuable information about stellar structure and evolution. It also aids in understanding the distance scale of the universe.

Globular clusters are groups of tightly bound stars orbiting galaxies. They serve as natural laboratories for studying the evolution of stars and galaxies. Specifically, these clusters can help researchers understand the formation history of early-type galaxies, as they are believed to be linked to intense periods of star formation.

NGC 1851, also known as Caldwell 73, is a notably bright and massive globular cluster situated approximately 39,000 light years from Earth. At about 9.2 billion years old, it has a metallicity of -1.27 dex and an estimated mass of 551,000 solar masses.

Earlier studies had identified 48 variable stars of the RR Lyrae type in NGC 1851 and suggested the presence of four or five long-period variables near the tip of the red giant branch (RGB).

To further explore the variable star population in NGC 1851, a team led by Armando Arellano Ferro from the National Autonomous University of Mexico used the Astronomical Observatory of Córdoba in Argentina.

Their observations revealed that of the 55 variables previously listed, eight were found to be field stars rather than cluster members. Additionally, for six variables, membership could not be confirmed due to lack of proper motion or blending with nearby bright stars.

The team discovered three new variables, with only one, V56, confirmed as a cluster member. This star was classified as an SX Phoenicis variable.

The study also validated the variability of two RR Lyrae stars of the RRab subtype and three long-period variables previously noted by Gaia satellite observations. All five confirmed variables were designated V57–V61.

Using the light curves of the RR Lyrae variables, the researchers estimated the metallicity of NGC 1851 to be around -1.35 dex and reaffirmed the cluster's distance as approximately 38,800 light years.