Abstract
<i>Context. <i/>Observations of SiO line emission in shocks in star-forming regions indicate that silicate dust destruction must be occurring in these dense regions. Current models rely on predictions for dust destruction by sputtering in C-type shock waves. However, J-type shocks may also be relevant for interpreting the widely-observed optical line emission from species such as O I and Fe II. <i>Aims. <i/>In this work we explore, for the first time, dust destruction in J-type shocks slower than 50 km s<sup>-1<sup/>. <i>Methods. <i/>We follow the dust trajectories throughout the shock using a model for the dust dynamics that allows us to solve the shock structure and at the same time calculate the degree of dust processing. We include the effects of sputtering in gas-grain collisions, and vaporisation and shattering in grain-grain collisions.<i>Results. <i/>We find that the amount of silicon released into the gas phase is a few percent. The dominant destructive process is vaporisation, not sputtering. The degree of dust destruction increases with the shock velocity but decreases as the preshock density increases. <i>Conclusions. <i/>Our results compare well with that of C-type shock models. J-type shocks are therefore reasonable candidates for an interpretation of SiO line emission in molecular outflows and jets.
Highlights
Dust constituents such as Fe, Mg and Si are known to be heavily depleted in diffuse and dense clouds
We show that dust destruction occurs in J-type shocks at levels comparable to that of C-type
In slow J shocks ( 100 km s−1) it is the gyration of grains around magnetic field lines, not the shock temperature, which is responsible for their destruction through both erosion by the gas and vaporisation in grain-grain collisions
Summary
Dust constituents such as Fe, Mg and Si are known to be heavily depleted in diffuse and dense clouds. Observations of supersonic jets and molecular outflows around YSOs attest to the presence of these refractory species in the gas phase, e.g. in the form of SiO or Fe II (Giannini et al 2004, 2006; Nisini et al 2007) This can be explained by models in which dust is destroyed in the shock waves initiated by jets and outflows. In this study we focus on the processing of dust grains in J-type shocks, i.e. mono-fluid shocks characterised by discontinuities (shock fronts) and high postshock temperatures Such shocks can exist even in the presence of a transverse magnetic field, provided that the shock velocity is higher than a critical velocity. We show that dust destruction occurs in J-type shocks at levels comparable to that of C-type
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