2025/09/12 by I. M. Skretas, Skretas, I. M., A. Karska +17
Engineering · Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Spacecraft and Cryogenic Technologies
paper · pdf · doi:10.48550/arxiv.2509.10256
openalex publication_date 2025/09/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
The main accretion phase of protostars is characterized by the ejection of material in the form of jets/outflows. External UV irradiation can potentially have a significant impact on the excitation conditions within these outflows. High-resolution observations in the mid-infrared allow us to investigate the details of those energetic processes through the emission of shock-excited H2 . Our aim is to spatially resolve H2 and ionic/atomic emission within the outflows of low-mass protostars, and investigate its origin in connection to shocks influenced by external ultraviolet irradiation. We analyze spectral maps of 5 Class I protostars in the Ophiuchus molecular cloud from the James Webb Space Telescope (JWST) Medium Resolution Spectrometer (MIRI/MRS). Four out of five protostars show strong H2, [\ionNeII], and [\ionFeII] emission associated with outflows/jets. Pure rotational H2 transitions from S(1) to S(8) are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ∼500-600 K and ∼1000-3000 K respectively. Both C-type shocks propagating at high pre-shock densities (nH ≥104 cm-3) and J-type shocks at low pre-shock densities (nH ≤103 cm-3) reproduce the observed line ratios. However, only C-type shocks produce sufficiently high column densities of H2, whereas predictions from a single J-type shock reproduce the observed rotational temperatures of the gas better. A combination of various types of shocks could play a role in protostellar outflows as long as UV irradiation is included in the models. The origin of this radiation is likely internal, since no significant differences in the excitation conditions of outflows are seen at various locations in the cloud.