SIMBAD references

Herschel observations suggest that the H₂O distribution in outflows from low-mass stars resembles the H₂ emission. It is still unclear which of the different excitation components that characterise the mid- and near-IR H₂ distribution is associated with H₂O. The aim is to spectrally resolve the different excitation components observed in the H₂ emission. This will allow us to identify the H₂ counterpart associated with H₂O and finally derive directly an H₂O abundance estimate with respect to H₂. We present new high spectral resolution observations of H₂ 0-0 S(4), 0-0 S(9), and 1-0 S(1) towards HH 54, a bright nearby shock region in the southern sky. In addition, new Herschel/HIFI H₂O (2₁₂-1₀₁) observations at 1670GHz are presented. Our observations show for the first time a clear separation in velocity of the different H₂ lines: the 0-0 S(4) line at the lowest excitation peaks at -7km/s, while the more excited 0-0 S(9) and 1-0 S(1) lines peak at -15km/s. H₂O and high-J CO appear to be associated with the H₂ 0-0 S(4) emission, which traces a gas component with a temperature of 700-1000K. The H₂O abundance with respect to H₂ 0-0 S(4) is estimated to be X(H₂O)<1.4x10^–5 in the shocked gas over an area of 13''. We resolve two distinct gas components associated with the HH 54 shock region at different velocities and excitations. This allows us to constrain the temperature of the H₂O emitting gas (≤1000K) and to derive correct estimates of H₂O abundance in the shocked gas, which is lower than what is expected from shock model predictions.