2025ApJ...985..225L

The near-infrared (NIR) emission of the youngest protostars still needs to be characterized to better understand the evolution of their accretion and ejection activity. We analyze James Webb Space Telescope NIRSpec 1.7-5.3 μm observations of two deeply embedded sources in the S68N protostellar core in Serpens. The North Central source exhibits a highly obscured spectrum (A_K ∼ 4.8 mag) that is modeled with a pre-main-sequence photosphere and a hot disk component. The photospheric parameters are consistent with a young, low-mass photosphere, as suggested by the low surface gravity, log g of 1.95 ±0.15 cm s^–2. The hot disk suggests that accretion onto the central protostellar embryo is ongoing, although prototypical accretion-tracing emission lines H I are not detected. The South Central source, which is even more embedded (A_K ∼ 8 mag; no continuum is detected shortward of 3.6 μm) appears to be driving the large-scale S68N protostellar outflow, and launches a collimated hot molecular jet detected in H₂ and CO rovibrational lines. Shock modeling of the H₂ (ro)vibrational lines establishes that fast C-type shocks (≥30 km s^–1), with high pre-shock density (≥10⁷ cm^–3), and strong magnetic field (b ∼ 3-10, where $B=b\,\times \,\sqrt{{n}_{{\rm{H}}}({\mathrm{cm}}^{-3})}\,\mu {\rm{G}}$) best match the data. The bright CO fundamental line forest suggests energetic excitation, with the contribution of non-LTE effects, i.e., irradiation pumping. Detected OH and CH⁺ rovibrational lines support this hypothesis. These two Class 0 protostars seem to be in very young evolutionary stages and still have to acquire the bulk of their final stellar masses. These results demonstrate that JWST enables unprecedented diagnostics of these first stages of the protostellar evolutionary phase.