Unveiling the Shock-Excited Molecular Environment in the Orion Protostar HOPS 370
We present near-infrared K-band ($1.94$--$2.52~μ$m) spectroscopy of the deeply embedded protostellar source HOPS\,370, obtained with the TIFR--ARIES Near Infrared Spectrometer (TANSPEC) on the 3.6-m Devasthal Optical Telescope (DOT). The spectrum is dominated by prominent molecular hydrogen ($\rm H_2$) ro-vibrational emission, with multiple transitions detected from the $1$--$0$ S, $2$--$1$ S, and $1$--$0$ Q branches. Using the intrinsically linked $\rm H_2$ $1$--$0$ Q(3) and $1$--$0$ S(1) transitions, which arise from the same upper energy level, we derive a visual extinction of $A_V = 23.24 \pm 1.25$ mag, corresponding to $A_K = 2.50 \pm 0.13$ mag, consistent with the embedded Class~0/I nature of the source. The diagnostic line ratio $F(2$--$1~{\rm S}(1))/F(1$--$0~{\rm S}(1)) = 0.12 \pm 0.01$ is consistent with thermal excitation and disfavors ultraviolet fluorescence as the dominant excitation mechanism. Assuming optically thin emission and local thermodynamic equilibrium, we derive an $\rm H_2$ excitation diagram that yields an excitation temperature of $2078 \pm 215$ K and a molecular hydrogen column density of $(1.93 \pm 0.93)\times10^{20}$ cm$^{-2}$. We further derive an ortho-to-para ratio of $2.45 \pm 0.21$, indicating substantial shock-driven thermal processing while remaining below the high-temperature equilibrium value of 3. Taken together, these diagnostics indicate that the molecular hydrogen emission in HOPS\,370 originates predominantly in warm, shock-heated gas most likely associated with its protostellar outflow. Our results demonstrate the diagnostic power of combined S- and Q-branch $\rm H_2$ spectroscopy for constraining the physical conditions and excitation history of deeply embedded protostellar systems.