Unveiling the Shock-Excited Molecular Environment in the Orion Protostar HOPS 370
Abstract
We present near-infrared K-band ($1.94−−2.52~μm) spectroscopy of the deeply embedded protostellar source HOPS 370, obtained with the TIFR−−ARIES Near Infrared Spectrometer (TANSPEC) on the 3.6−m Devasthal Optical Telescope (DOT). The spectrum is dominated by prominent molecular hydrogen (\rm H_2$) ro-vibrational emission, with multiple transitions detected from the $1−−0$ S, $2−−1$ S, and $1−−0$ Q branches. Using the intrinsically linked H2 $1−−0$ Q(3) and $1−−0$ S(1) transitions, which arise from the same upper energy level, we derive a visual extinction of AV = 23.24 ± 1.25 mag, corresponding to AK = 2.50 ± 0.13 mag, consistent with the embedded Class~0/I nature of the source. The diagnostic line ratio F(2--1 S(1))/F(1--0 S(1)) = 0.12 ± 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 H2 excitation diagram that yields an excitation temperature of 2078 ± 215 K and a molecular hydrogen column density of (1.93 ± 0.93)×1020 cm−2. We further derive an ortho-to-para ratio of 2.45 ± 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 H2 spectroscopy for constraining the physical conditions and excitation history of deeply embedded protostellar systems.
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BibTeX
@misc{dutta2026unveiling,
title = {{Unveiling the Shock-Excited Molecular Environment in the Orion Protostar HOPS 370}},
author = {Somnath Dutta and Koshvendra Singh and Devendra K Ojha and Saurabh Sharma and Tarak Chand and Manojit Chakraborty and Kartik Gokhe and Joe P. Ninan and Jyotirmoy Dey},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38192},
eprint = {2610.38192},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38192},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Unveiling the Shock-Excited Molecular Environment in the Orion Protostar HOPS 370
AU - Somnath Dutta
AU - Koshvendra Singh
AU - Devendra K Ojha
AU - Saurabh Sharma
AU - Tarak Chand
AU - Manojit Chakraborty
AU - Kartik Gokhe
AU - Joe P. Ninan
AU - Jyotirmoy Dey
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38192
UR - https://arxiv.org/abs/2610.38192
AB - We present near-infrared K-band ($1.94−−2.52~μm) spectroscopy of the deeply embedded protostellar source HOPS 370, obtained with the TIFR−−ARIES Near Infrared Spectrometer (TANSPEC) on the 3.6−m Devasthal Optical Telescope (DOT). The spectrum is dominated by prominent molecular hydrogen (\rm H_2$) ro-vibrational emission, with multiple transitions detected from the $1−−0$ S, $2−−1$ S, and $1−−0$ Q branches. Using the intrinsically linked 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 ± 1.25 mag, corresponding to A_K = 2.50 ± 0.13 mag, consistent with the embedded Class~0/I nature of the source. The diagnostic line ratio F(2--1 S(1))/F(1--0 S(1)) = 0.12 ± 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 H_2 excitation diagram that yields an excitation temperature of 2078 ± 215 K and a molecular hydrogen column density of (1.93 ± 0.93)×10^20 cm^−2. We further derive an ortho-to-para ratio of 2.45 ± 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 H_2 spectroscopy for constraining the physical conditions and excitation history of deeply embedded protostellar systems.
ER -