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|Title:||The density structure of the L1157 molecular outflow||Authors:||Gómez-Ruiz, A. I.
|Issue Date:||2015||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||446||Issue:||4||First Page:||3346||Abstract:||We present a multiline CS survey towards the brightest bow-shock B1 in the prototypical chemically active protostellar outflow L1157. We made use of (sub-)mm data obtained in the framework of the Chemical HErschel Surveys of Star forming regions and Astrochemical Surveys at IRAM (ASAI) key science programs. We detected <SUP>12</SUP>C<SUP>32</SUP>S, <SUP>12</SUP>C<SUP>34</SUP>S, <SUP>13</SUP>C<SUP>32</SUP>S, and <SUP>12</SUP>C<SUP>33</SUP>S emissions, for a total of 18 transitions, with E<SUB>u</SUB> up to ̃180 K. The unprecedented sensitivity of the survey allows us to carefully analyse the line profiles, revealing high-velocity emission, up to 20 km s<SUP>-1</SUP> with respect to the systemic. The profiles can be well fitted by a combination of two exponential laws that are remarkably similar to what previously found using CO. These components have been related to the cavity walls produced by the ̃2000 yr B1 shock and the older (̃4000 yr) B2 shock, respectively. The combination of low- and high-excitation CS emission was used to properly sample the different physical components expected in a shocked region. Our CS observations show that this molecule is highlighting the dense, n<SUB>H<SUB>2</SUB></SUB> = 1-5 × 10<SUP>5</SUP> cm<SUP>-3</SUP>, cavity walls produced by the episodic outflow in L1157. In addition, the highest excitation (E<SUB>u</SUB> ≥ 130 K) CS lines provide us with the signature of denser (1-5 × 10<SUP>6</SUP> cm<SUP>-3</SUP>) gas, associated with a molecular reformation zone of a dissociative J-type shock, which is expected to arise where the precessing jet impacting the molecular cavities. The CS fractional abundance increases up to ̃10<SUP>-7</SUP> in all the kinematical components. This value is consistent with what previously found for prototypical protostars and it is in agreement with the prediction of the abundances obtained via the chemical code Astrochem.||Acknowledgments:||We thank the anonymous referee for the detailed comments which helped to improve the clarity of this paper. We are grateful to S. Cabrit for useful discussion and suggestions. The Italian authors gratefully acknowledge the support from the Italian Space Agency (ASI) through the contract I/005/011/0, which also provided the fellowships of A.I Gómez-Ruiz and G. Busquet. GB is supported by the Spanish MICINN grant AYA2011-30228-C03-01 (co-funded with FEDER funds). 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; The Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiología (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.||URI:||http://hdl.handle.net/20.500.12386/23760||URL:||https://academic.oup.com/mnras/article/446/4/3346/2892333||ISSN:||0035-8711||DOI:||10.1093/mnras/stu2311||Bibcode ADS:||2015MNRAS.446.3346G||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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