Paper detail

Discovery of a primordial water reservoir in the envelope of HH211

We report on the detection of a rich water reservoir in the protostellar envelope of the Class 0 source HH211. In striking contrast to all other molecules detected with Herschel/PACS, water emission peaks around the central source where both ortho and para forms are detected. The measured ortho-to-para ratio of just 0.65 indicates formation of water-ice at very low temperatures and a non-destructive photo-desorption process around the protostar. While part of the water emission is likely related to collisional excitation, the centralized morphology around the protostar suggests that radiative excitation is also significant, despite the fact that radiation appears to have a very different impact on the water molecules when compared to the terminal outflow shocks. The very low ortho-to-para ratio suggests that water around the protostar originates from primordial envelope material that has never been thermally processed before.