Characterization of the Blue Straggler Star Populations, through Statistical, Photometric, and Spectral Energy Distribution Analysis, in the Old Open Cluster: NGC 2243

Abstract We present a statistical, photometric, and spectral energy distribution (SED) analysis of the poorly studied old open cluster: NGC 2243, to characterize its blue straggler star (BSS) population. We applied ensemble-based unsupervised machine learning methods to estimate the membership probabilities using Gaia Data Release 3 (DR3) astrometric data. NGC 2243 is an open cluster that is 3.67 Gyr old with a metallicity of −0.375 dex, situated at a distance of 3.65 kpc. By analyzing the position of cluster members on the color–magnitude diagram using MIST isochrones, we have identified 12 potential BSSs in NGC 2243. We fitted the radial surface density profile and investigated the dynamical state and mass segregation effect of the cluster. It is found that the BSSs are significantly concentrated within the central region. We used data from Swift/UVOT, Gaia DR3, Pan-STARRS1 DR2, 2MASS, and WISE to fit the SEDs of the 12 identified BSSs using VOSA. We estimated the masses of the BSSs from the Hertzsprung–Russell diagram and found that they ranged from 1.25 to 2.22 M ☉ . Consequently, we concluded that the BSSs likely gained 0.11–1.08 M ☉ through the mass transfer or merger channels. We discovered a hot companion associated with one BSS candidate, which has a temperature of 19,000 K, a luminosity of 0.55 L ☉ , and a radius of 0.065 R ☉ . The hot companion is probably a white dwarf, with its mass estimated to be approximately 0.18–0.20 M ☉ and an age of 186 Myr, suggesting it is a post-mass-transfer (Case A or Case B) system.