Herschel-PACS full spectral range spectrum of the B1 shock in the L1157 outflow
M. Benedettini, B. Lefloch, C. Codella, S. Cabrit, C. Ceccarelli, J. Cernicharo, A. M di Giorgio, T. Giannini, B. Nisini, M. Vasta, and the CHESS team
We present the Herschel-PACS 55-210 microns spectrum of the B1 shock in the L1157 outflow obtained within the CHESS (Chemical Herschel Survey of Star forming regions) Key Program, aimed at obtaining an accurate census of the molecular content in star forming regions. B1 is the brightest shock episode in the blue lobe of the L1157 chemically active outflow. Previous interferometric maps have already shown a clumpy structure of the molecular gas with different species peaking at different positions in the bow shock, indicating a variation in the physical conditions and/or the chemical composition of the molecular gas. The spatial resolution and the frequency range of the PACS spectrometer allows to map the warm gas traced by far-infrared molecular lines with an unprecedented detail.
The PACS spectra of the B1 bow shock show emission lines from CO, H2O, OH and [OI]. We used Large Velocity Gradient models to obtain the physical parameters of the emitting gas. From the analysis of high J- CO transitions we derived a gas temperature of 1000 K and a density of 2´104 cm-3. The emission of CO, H2O, OH, [OI] and Spitzer [FeII] peak at the rear of the bow shock apex. All this indicates that dissociative (J-type) shocks are responsible of the line emission detected in the PACS range.