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The CHESS Survey of the L1157-B1 Shock Region: CO Spectral Signatures of Jet-driven Bow Shocks

Lefloch, B. and Cabrit, S. and Busquet, G. and Codella, C. and Ceccarelli, C. and Cernicharo, J. and Pardo, J. R. and Benedettini, M. and Lis, D. C. and Nisini, B. (2012) The CHESS Survey of the L1157-B1 Shock Region: CO Spectral Signatures of Jet-driven Bow Shocks. Astrophysical Journal Letters, 757 (2). Art. No. L25. ISSN 2041-8205. doi:10.1088/2041-8205/757/2/L25.

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The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity-velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. Over the course of the CHESS Key Program, we have observed toward the bright bow shock region L1157-B1, the CO rotational transitions between J = 5-4 and J = 16-15 with HIFI, and the J = 1-0, 2-1, and 3-2 with the IRAM 30 m and the Caltech Submillimeter Observatory telescopes. We find that all the line profiles I_(CO)(v) are well fit by a linear combination of three exponential laws ∝ exp (– |v/v_0|) with v_0 = 12.5, 4.4, and 2.5 km s^(–1). The first component dominates the CO emission at J ≥ 13, as well as the high-excitation lines of SiO and H_(2)O. The second component dominates for 3 ≤ J up ≤ 10 and the third one for J_up ≤ 2. We show that these exponentials are the signature of quasi-isothermal shocked gas components: the impact of the jet against the L1157-B1 bow shock (T_k ≃ 210 K), the walls of the outflow cavity associated with B1 (T_k ≃ 64 K), and the older cavity L1157-B2 (T_k ≃ 23 K), respectively. Analysis of the CO line flux in the large-velocity gradient approximation further shows that the emission arises from dense gas (n(H_2) ≥ 10^(5)-10^(6) cm^(–3)) close to LTE up to J = 20. We find that the CO J = 2-1 intensity-velocity relation observed in various other molecular outflows is satisfactorily fit by similar exponential laws, which may hold an important clue to their entrainment process.

Item Type:Article
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Codella, C.0000-0003-1514-3074
Ceccarelli, C.0000-0001-9664-6292
Lis, D. C.0000-0002-0500-4700
Additional Information:© 2012 American Astronomical Society. Received 2012 June 30; accepted 2012 August 20; published 2012 September 12. We thank R. Bachiller and T. Downes for providing us with the observational data presented in Figure 3. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France, and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astron´omico Nacional (IGN), Centro de Astrobiolog´ıa (CSIC-INTA); Sweden: Chalmers University of Technology—MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University—Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. C. Codella and C. Ceccarelli acknowledge the financial support from the COST Action CM0805 “The Chemical Cosmos.” S. Cabrit and C. Ceccarelli acknowledge the financial support from the French spatial agency CNES. G. Busquet is supported by an Italian Space Agency (ASI) fellowship under contract number I/005/007. B. Lefloch thanks the Spanish MEC for funding support through grant SAB2009-0011. J. Cernicharo thanks the Spanish MICINN for funding support through grants AYA2009-07304 and CSD2009-00038. Support for this work was provided by NASA through an award issued by JPL/Caltech. The CSO is supported by the National Science Foundation under the contract AST-08388361.
Funding AgencyGrant Number
COST ActionCM0805
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Agenzia Spaziale Italiana (ASI)I/005/007
Ministerio de Educación y Ciencia (MEC)SAB2009-0011
Ministerio de Ciencia e Innovación (MCINN)AYA2009-07304
Ministerio de Ciencia e Innovación (MCINN)CSD2009-00038
Subject Keywords:ISM: jets and outflows; ISM: molecules; stars: formation
Issue or Number:2
Record Number:CaltechAUTHORS:20121019-135821350
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Official Citation:The CHESS Survey of the L1157-B1 Shock Region: CO Spectral Signatures of Jet-driven Bow Shocks B. Lefloch et al. 2012 ApJ 757 L25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34993
Deposited By: Jason Perez
Deposited On:22 Oct 2012 14:59
Last Modified:09 Nov 2021 23:11

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