2011A&A...531L...1K

Herschel-HIFI observations of water in the low-mass star-forming object L1448-MM, known for its prominent outflow, are presented, as obtained within the ``Water in star-forming regions with Herschel'' (WISH) key programme. Six H<sub>2</sub><sup>16</sup>O lines are targeted and detected (E<sub>up</sub>/k<sub>B</sub>∼50-250K), as is CO J=10-9 (E<sub>up</sub>/k<sub>B</sub>∼305K), and tentatively H<sub>2</sub><sup>18</sup>O 1<sub>10</sub>-1<sub>01</sub> at 548GHz. All lines show strong emission in the ``bullets'' at |3|>50km/s from the source velocity, in addition to a broad, central component and narrow absorption. The bullets are seen much more prominently in H₂O than in CO with respect to the central component, and show little variation with excitation in H₂O profile shape. Excitation conditions in the bullets derived from CO lines imply a temperature >150K and density >10⁵cm^–3, similar to that of the broad component. The H₂O/CO abundance ratio is similar in the ``bullets'' and the broad component, ∼0.05-1.0, in spite of their different origins in the molecular jet and the interaction between the outflow and the envelope. The high H<sub>2</sub>O abundance indicates that the bullets are H<sub>2</sub> rich. The H<sub>2</sub>O cooling in the ``bullets'' and the broad component is similar and higher than the CO cooling in the same components. These data illustrate the power of Herschel-HIFI to disentangle different dynamical components in low-mass star-forming objects and determine their excitation and chemical conditions.