Astron. Astrophys. 321, 293-304 (1997)

SiO production in interstellar shocks ^*

P. Schilke ¹, C.M. Walmsley ², G. Pineau des Forêts ³ and D.R. Flower <sup>4

1</sup> I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
² Osservatorio di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
³ DAEC, Observatoire de Paris, F-92195 Meudon Principal Cedex, France
⁴ Physics Department, The University, Durham DH1 3LE, UK

Received 22 April 1996 / Accepted 19 August 1996

Abstract

We study the production of SiO in the gas phase of molecular outflows, through the sputtering of Si-bearing material in grains. The sputtering is driven by neutral particle impact on charged grains in C-type shocks, at the speed corresponding to ambipolar diffusion. Shock speeds in the range and preshock densities have been investigated. Sputtering of Si-bearing material in both the cores and the mantles of the grains is considered. We find that, for of approximately 25 km s^-1 and of the order cm^-3, column densities of SiO similar to those observed in molecular outflow regions can be generated by either mechanism. Impact by particles heavier than helium dominates the core-sputtering process for shock velocities of this order. The profiles of rotational transitions of SiO are computed and compared with observations of molecular outflows.

Key words: molecular processes shock waves ISM: abundances; jets and outflows; molecules

* Tables 1 and 2 are available in electronic form at CDS via ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: G. Pineau des Forêts

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Contents

• 1. Introduction
• 2. Observations of the constituents of refractory materials in molecular clouds
• 3. The model
  • 3.1. Sputtering of grain cores
  • 3.2. Sputtering of grain mantles
  • 3.3. Dissociation of neutral molecules in collisions with charged grains
  • 3.4. Gas-phase chemistry of silicon-bearing species
  • 3.5. Calculation of line profiles
• 4. Results
  • 4.1. Sputtering of refractory grain cores
  • 4.2. Sputtering of Si-bearing material in grain mantles
• 5. Concluding remarks
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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