Constructing the Hertzsprung-Russell Diagram of the Northern and Southern Regions of the NGC 2264 Star Cluster Using Gaia

Abstract

NGC 2264, a young open cluster in the Monoceros association, hosts active star formation in its northern and southern regions. Using ~230 stars with FLAMINGOS near-infrared spectra, Spitzer IR photometry, 2MASS N-IR photometry, and Gaia optical astrometry, we examine the cluster’s structure, evolutionary state, and membership. Gaia parallaxes refine the mean distances to 715 ± 21 pc (North) and 731 ± 20 pc (South). After applying distance constraints and accounting for uncertainties, 134 sources remain for Hertzsprung–Russell diagram (HRD) construction using optical and near-IR photometry. The HRDs indicate that the South is younger, with a mean isochronal age of 2.42 ± 0.36 Myr, compared to 3.10 ± 0.39 Myr in the North, consistent with a hierarchical star formation scenario. Additionally, they show a predominance of pre–main sequence stars in the South and more evolved PMS stars in the North. These results provide a refined characterization of NGC 2264’s stellar populations, highlighting its spatial, kinematic, and evolutionary properties.