2026/08/03 by Siyi Feng, Hauyu Baobab Liu, Yang Lu +11
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.1051/0004-6361/202659452
11 pages, 5 figures, accepted by Astronomy & Astrophysics
arxiv created 2026/08/03 · arxiv updated 2026/08/04
Protostellar outflow shocks reshape local dust properties and molecular chemistry. The L1157 outflow is an archetypal chemically rich shocked region, but the thermal dust associated with its successive shocks has remained unresolved because molecular-line contamination obscures the broadband continuum. We obtained new James Clerk Maxwell Telescope (825--906 μm) spectral-line observations and Submillimeter Array (1.1--1.4 mm) continuum observations toward L1157 B0-B1-B2, probing spatial scales from 0.4 pc to 1200 au. After removing molecular-line contamination on a pixel-by-pixel basis, we derived the dust temperature, column density, and dust opacity index from continuum data spanning 70 μm to 1.3 mm. The line-corrected continuum maps reveal the dust distribution across successive shocks. The dust opacity index (β≈1.8--2.3) indicates that grains have not grown to millimeter sizes throughout the shocked regions. Combined with previous \rm NH3 observations, we find that the dust emission resolves into compact clumps along the precessing jet, whereas gaseous \rm NH3 peaks at the shock fronts, reaching abundances of ∼10-5 relative to \rm H2, even where the 0.85 and 1.3 mm dust emission is detected at only 3--5σ. Our newly developed physicochemical shock model shows that \rm NH3 forms predominantly on grain surfaces and is released by shock-induced sputtering, with the highest abundances occurring where post-shock re-adsorption remains inefficient. These results establish spatially resolved dust continuum imaging as a direct observational probe of grain evolution and provide new observational constraints on dust-gas interactions in protostellar shocks.