Water in low-mass star-forming regions with Herschel (WISH-LM) - High-velocity H2O bullets in L1448-MM observed with HIFI

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(2)(16)O lines are targeted and detected (E(up)/k(B) similar to 50-250 K), as is CO J = 10-9 (E(up)/k(B) similar to 305 K), and tentatively H(2)(18)O 1(10)-1(01) at 548 GHz. All lines show strong emission in the "bullets" at vertical bar upsilon vertical bar > 50 km s(-1) from the source velocity, in addition to a broad, central component and narrow absorption. The bullets are seen much more prominently in H(2)O than in CO with respect to the central component, and show little variation with excitation in H(2)O profile shape. Excitation conditions in the bullets derived from CO lines imply a temperature > 150 K and density > 10(5) cm(-3), similar to that of the broad component. The H(2)O/CO abundance ratio is similar in the "bullets" and the broad component, similar to 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 H2O abundance indicates that the bullets are H(2) rich. The H(2)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.