Letter to the Editor

The CHESS spectral survey of star forming regions: Peering into the protostellar shock L1157-B1^*

II. Shock dynamics

¹ Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France e-mail: lefloch@obs.ujf-grenoble.fr
² Observatoire de Paris-Meudon, LERMA UMR CNRS 8112. Meudon, France
³ INAF, Osservatorio Astrofisico di Arcetri, Firenze, Italy
⁴ Center for Astrophysics, Cambridge MA, USA
⁵ Centro de Astrobiología, CSIC-INTA, Madrid, Spain
⁶ CESR, Université Toulouse 3 and CNRS, Toulouse, France
⁷ INAF, Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
⁸ IPAC, NASA Herschel Science Center, CalTech, USA
⁹ School of Physics and Astronomy, University of Leeds, Leeds, UK
¹⁰ Institut de Radio Astronomie Millimétrique, Grenoble, France
¹¹ Johns Hopkins University, Baltimore MD, USA
¹² INAF, Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
¹³ Max-Planck-Institut für Radioastronomie, Bonn, Germany
¹⁴ Department of Physics and Astronomy, University College London, London, UK
¹⁵ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, Floirac, France
¹⁶ California Institute of Technology, Pasadena, USA
¹⁷ University of Michigan, Ann Arbor, USA
¹⁸ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Amsterdam, The Netherlands
¹⁹ Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
²⁰ IGN Observatorio Astronómico Nacional, Spain
²¹ Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
²² SRON, Groningen, The Netherlands
²³ Max Planck Institut für Astronomie, Heidelberg – Germany Ohio State University, Columbus, OH, USA
²⁴ Physikalisches Institut, Universität zu Köln, Köln, Germany
²⁵ Leiden Observatory, Leiden University, Leiden, The Netherlands
²⁶ IRAM, Granada, Spain
²⁷ Department of Astronomy, Stockholm University, Stockholm, Sweden
²⁸ Northrop Grumman Aerospace Systems, Redondo Beach, CA 90278, USA

Received: 31 March 2010
Accepted: 30 April 2010

Abstract

Context. The outflow driven by the low-mass class 0 protostar L1157 is the prototype of the so-called chemically active outflows. The bright bowshock B1 in the southern outflow lobe is a privileged testbed of magneto-hydrodynamical (MHD) shock models, for which dynamical and chemical processes are strongly interdependent.

Aims. We present the first results of the unbiased spectral survey of the L1157-B1 bowshock, obtained in the framework of the key program “Chemical HErschel Surveys of star forming regions” (CHESS). The main aim is to trace the warm and chemically enriched gas and to infer the excitation conditions in the shock region.

Methods. The CO 5-4 and o-H₂O 1₁₀–1₀₁ lines have been detected at high-spectral resolution in the unbiased spectral survey of the HIFI-band 1b spectral window (555–636 GHz), presented by Codella et al. in this volume. Complementary ground-based observations in the submm window help establish the origin of the emission detected in the main-beam of HIFI and the physical conditions in the shock.

Results. Both lines exhibit broad wings, which extend to velocities much higher than reported up to now. We find that the molecular emission arises from two regions with distinct physical conditions : an extended, warm (100 K), dense (3 × 10⁵ cm^-3) component at low-velocity, which dominates the water line flux in Band 1; a secondary component in a small region of B1 (a few arcsec) associated with high-velocity, hot (>400 K) gas of moderate density ((1.0–3.0) × 10⁴ cm^-3), which appears to dominate the flux of the water line at 179μm observed with PACS. The water abundance is enhanced by two orders of magnitude between the low- and the high-velocity component, from 8 × 10^-7 up to 8 × 10^-5. The properties of the high-velocity component agree well with the predictions of steady-state C-shock models.