Characteristics of XUE stars. In all panels, XUE stars are color-coded and labeled for clarity. The Orion Nebula young stars are represented by blue plus symbols, and NGC 6357 young stars are shown as gray crosses (Getman et al. 2005; Broos et al. 2013; King et al. 2013; Townsley et al. 2019; Getman et al. 2022). (a, b) UKIRT/VVV NIR color-magnitude and color-color diagrams. PARSEC 1.2S PMS isochrones for 0.7 and 2 Myr are shown as solid and dashed curves, respectively. Reddening vectors corresponding to A_V = 10 mag are drawn as solid and dashed lines, originating from G0 stars at 0.7 Myr and F0 stars at 2 Myr. (c) Spitzer-IRAC MIR color-color diagram of NGC 6357 young stars with known IRAC photometry. Gray squares represent known disky stars, while purple circles indicate diskless stars (Povich et al. 2013). (d) Absolute K-band magnitude (uncorrected for extinction) as a function of stellar mass. (e) Intrinsic X-ray luminosity as a function of stellar mass. (f) X-ray column density plotted against visual-band extinction. The names of the sources are displayed on the markers and are visible when zooming in.