Volume 539, March 2012
|Number of page(s)||6|
|Published online||22 February 2012|
1 INAF – Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Roma, Italy
2 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble UMR 5274, 38041 Grenoble, France
3 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
4 LERMA, Observatoire de Paris, UMR 8112 du CNRS, ENS, UPMC, UCP, 61 avenue de l’Observatoire, 75014 Paris, France
5 INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
6 CAB, INTA-CSIC, Department of Astrophysics, Crta Torrejón km 4. Torrejón de Ardoz, Madrid, Spain
Received: 23 December 2011
Accepted: 1 February 2012
Outflows generated by protostars heavily affect the kinematics and chemistry of the hosting molecular cloud through strong shocks that enhance the abundance of some molecules. L1157 is the prototype of chemically active outflows, and a strong shock, called B1, is taking place in its blue lobe between the precessing jet and the hosting cloud. We present the Herschel-PACS 55–210 μm spectra of the L1157-B1 shock, showing emission lines from CO, H2O, OH, and [O i]. The spatial resolution of the PACS spectrometer allows us to map the warm gas traced by far-infrared (FIR) lines with unprecedented detail. The rotational diagram of the high-Jup CO lines indicates high-excitation conditions (Tex ≃ 210 ± 10 K). We used a radiative transfer code to model the hot CO gas emission observed with PACS and in the CO (13–12) and (10–9) lines measured by Herschel-HIFI. We derive 200 < Tkin < 800 K and n ≥ 105 cm-3. The CO emission comes from a region of about 7′′ located at the rear of the bow shock where the [O i] and OH emission also originate. Comparison with shock models shows that the bright [O i] and OH emissions trace a dissociative J-type shock, which is also supported by a previous detection of [FeII] at the same position. The inferred mass-flux is consistent with the “reverse” shock where the jet is impacting on the L1157-B1 bow shock. The same shock may contribute significantly to the high-Jup CO emission.
Key words: stars: formation / ISM: individual objects: L1157-B1 / ISM: molecules / ISM: jets and outflows
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2012
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