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Strong magnetic fields in bipolar outflows

  • M. D. Smith (a1), P. W. J. L. Brand (a2) and A. Moorhouse (a3)

Abstract

A supersonic wind from a young star will produce regions of strong magnetic field in the stellar environment. The associated shocks compress the molecular gas, increasing the density n, pressure p, and field B. Crucially, the Alfvén speed, v A ∝ B/n1/2, is also increased since the total shock compression is approximately of the form B ∝ n. But is there any evidence for such high v A - or ‘active cloud’ - regions within bipolar outflows? We indicate below one implication which has important observable consequences: fast shocks of low Alfvén number (v/v A ) now arise. With a low ionization level, the C-shock structure is qualitatively different from the high Alfvén number flows which are common to ‘quiescent cloud’ conditions. The magnetic-field cushioning now allows molecular hydrogen to survive very fast shocks and broad H2 lines are feasible. We display results which show that the resolved broad lines and line ratio properties in the OMC-1 outflow can be explained with fast bow shocks moving through such active regions.

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Copyright

References

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Brand, P.W.J.L., Moorhouse, A., Burton, M.G., Geballe, T.R., Bird, M., & Wade, R., 1988. Astrophys. J. Letters 334, L103.
Brand, P., Toner, M.P. et al. 1989. M.N.R.A.S. 236, 929.
Brand, P., Toner, M.P. et al. 1989. M.N.R.A.S. 237, 1009.
Draine, B.T., Roberge, W.G. & Dalgarno, A., 1983. Ap. J., 264, 485.
Smith, M.D. & Brand, P.W.J.L., 1990a. M.N.R.A.S. 242, 495.
Smith, M.D. & Brand, P.W.J.L., 1990b. M.N.R.A.S. 245, 108.
Smith, M.D., Brand, P.W.J.L. & Moorhouse, A., 1990a & 1990b. M.N.R.A.S. submitted

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