A numerical simulation of a wind/molecular clump interaction |
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| Authors: | A C Raga J Cantó S Curiel & S Taylor |
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| Institution: | Instituto de Astronomía, UNAM, Ap. 70-264, 04510 México, DF, México,;Department of Physics and Astronomy, University College, Gower Street, London WC1E 6BT |
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| Abstract: | It has been pointed out in the past that it is impossible to accelerate molecular material to velocities ≥ 25 km s?1 with gasdynamic shocks without dissociating the gas. Because of this, it has been argued that observations of molecular emission with radial velocities ～ 20–100 km s?1 imply the presence of 'C-shocks' (which have much lower post-shock temperatures, and therefore do not dissociate the gas) and the existence of strong (～ 10–100 μG) magnetic fields. In this paper, we discuss an alternative mechanism for accelerating molecular material to high velocities: a high-velocity, low-density wind drives a non-dissociative shock (with shock velocity v cs ≤ 25 km s?1) into a high-density, molecular clump. Once this shock wave has gone through the clump, the molecular material is moving at a velocity ～ v cs and has a gas pressure approximately equal to the ram pressure of the impinging wind. The compressed molecular clump can now be accelerated directly by the ram pressure of the wind (without the passage of further shocks through the molecular material), and will eventually move at the wind velocity. This mechanism has been previously invoked to explain high-velocity molecular emission. However, numerical simulations have shown that a wind/clump interaction leads to the fragmentation of the clump before it can be accelerated to large velocities. In our numerical simulation (which includes an approximate treatment of the relevant microphysics) we find that the fragments that are produced are still largely molecular, and that they are rapidly accelerated to velocities comparable to the wind velocity. We therefore conclude that a wind/molecular clump interaction is indeed a valid mechanism for producing high-velocity molecular features. |
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| Keywords: | hydrodynamics shock waves stars: formation stars: mass-loss |
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