Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1H040

Dense cavity walls traced by CS in the L1157-B1 protostellar shocked region

Gomez-Ruiz, Arturo (INAF-Osservatorio Astrofisico di Arcetri)
Codella, Claudio (INAF-Osservatorio Astrofisico di Arcetri)
Lefloch, Bertrand (Institut de Planetologie et d\'Astrophysique de Grenoble (IPAG))
Benedettini, Milena (INAF-Istituto di Astrofisica e Planetologia Spaziali)
Busquet, Gemma (INAF-Istituto di Astrofisica e Planetologia Spaziali)
Nisini, Brunella (INAF-Osservatorio Astronomico di Roma)
Ceccarelli, Cecilia (Institut de Planetologie et d\'Astrophysique de Grenoble (IPAG))
Cabrit, Sylvie (LERMA, Observatoire de Paris)
Viti, Serena (University College London (UCL))

In the framework of the CHESS Key Program, an unbiased spectral survey performed with Herschel and IRAM, in the frequency range from 97 to 600 GHz, have provided a chemical census of the protostellar shock L1157-B1. Here we focus on the study of carbon monosulfide (CS), a standard tracer of high-density gas. We have detected a total of 18 emission lines, with E_u up to 183 K, due to four isotopologues (^12C^32S, ^12C^34S, ^13C^32S, and ^12C^33S). The unprecedented sensitivity of the survey allow us to carefully analyze the line profiles. These profiles can be well fitted by two exponential laws: I ∝ exp(−|v/v0|) with v0 = 4.4, and 2.5 km s−1. Remarkably these two exponential laws are the same as those found in the CO line profiles by Lefloch et al. (2012), and named g2 and g3 components, respectively. These components have been related to the cavity walls produced by the B1 shock and the older B2 shock, respectively. An important characteristic of the lines profiles is that the emission of high-J CS transitions (E_u > 60 K) comes only from the g2 component. Using the LVG approximation, the CS solutions constrain n >= 10^4.5 cm^-3. In addition, when contrasted with the CO results (that already constrained T_k of 90 K and 40 K for g2 and g3, respectively), we see that the LVG can provide strong constrains to the gas density, in this case about 5 x 10^5 cm^-3 for both g2 and g3 components. Thus, the combination of CO and CS is a powerful tool to constrain both n and T_k. Our CS observations show therefore that this molecule is highlighting the dense cavity walls produced by the episodic outflow.

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