X-Ray and Infrared Observations of Embedded Young Stars in NGC 2264

Images of the NGC 2264 star-forming region, which we have acquired with the XMM-Newton spacecraft, reveal strong X-ray emission from three deeply embedded (A_V>=10 mag) young stellar objects in the vicinity of Allen's infrared source (AFGL 989 = IRS 1) and Castelaz & Grasdalen's infrared source (RNO-EW = IRS 2). Thermal plasma models for the brightest source in X-rays, located 11" southwest of Allen's star, yield a quasi-steady luminosity of L_X=10³³ ergs s^-1 and an extraordinarily high X-ray temperature of 100 MK. The high temperature is consistent with the presence of emission lines of Fe XXV and Fe XXVI at photon energies of 6.7 and 6.9 keV, respectively. An even higher temperature of nearly ~140 MK was observed during the rise phase of a powerful impulsive X-ray flare of another young star in the IRS 2 region. Moderate-resolution near-infrared (1-4 μm) spectra of the embedded objects, obtained at the NASA Infrared Telescope Facility, exhibit deep water ice absorption bands, as well as a variety of emission and absorption features of H I, CO, and both neutral and ionized metals.