2010A&A...521L..30K

``Water In Star-forming regions with Herschel'' (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC 1333 in several H₂¹⁶O, H₂¹⁸O, and CO transitions. Line profiles are resolved for five H₂¹⁶O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20km/s), medium-broad (∼5-10km/s), and narrow (<5km/s) components. The H₂¹⁸O emission is only detected in broad 1₁₀-1₀₁ lines (>20km/s), indicating that its physical origin is the same as for the broad H₂¹⁶O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (≲1000AU) and large scales along the outflow cavity walls (∼10000AU). The H₂O line profiles are compared to CO line profiles to constrain the H₂O abundance as a function of velocity within these shocked regions. The H₂O/CO abundance ratios are measured to be in the range of ∼0.1-1, corresponding to H₂O abundances of ∼10^–5-10^–4 with respect to H₂. Approximately 5-10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities.