Letter to the Editor
Water in low-mass star-forming regions with Herschel (WISH-LM)⋆
High-velocity H2O bullets in L1448-MM observed with HIFI⋆⋆
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
3 Observatorio Astronómico Nacional (IGN), Calle Alfonso XII, 3. 28014 Madrid, Spain
4 INAF - Osservatorio Astronomico di Roma, 00040 Monte Porzio catone, Italy
5 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
Received: 29 March 2011
Accepted: 18 May 2011
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 HO lines are targeted and detected (Eup/kB ~ 50–250 K), as is CO J = 10–9 (Eup/kB ~ 305 K), and tentatively HO 110–101 at 548 GHz. All lines show strong emission in the “bullets” at |3| > 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 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 >150 K and density >105 cm-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 H2O abundance indicates that the bullets are H2 rich. The H2O 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.
Key words: astrochemistry / stars: formation / ISM: molecules / ISM: jets and outflows / ISM: individual objects: L1448
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendices and Tables 2 and 3 are available in electronic form at http://www.aanda.org
© ESO, 2011