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Astron. Astrophys. 343, 558-570 (1999)


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Deflection of stellar jets by ambient magnetic fields

J.D. Hurka 1, J. Schmid-Burgk 1 and P.E. Hardee 2

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA

Received 26 January 1998 / Accepted 11 November 1998

Abstract

We deal with the question whether the deflection of stellar jets/outflows that is observed for example in L 1221 can be caused by strong ambient magnetic fields. We present results of fully three-dimensional (3D) numerical magnetohydrodynamics (MHD) simulations of adiabatic jets propagating into an initially homogeneous medium containing an oblique magnetic field. In our model, the jet is longitudinally magnetized by a field of the strength of the x-component of the ambient magnetic field. We varied the jet velocity [FORMULA] (in the range 2 to 40 km s-1), the ambient magnetic field strength [FORMULA] (50, 100 µG), and the angle [FORMULA] ([FORMULA] to [FORMULA]) between the initial jet velocity and the ambient field to find the dependence of the critical velocity [FORMULA] (up to which a jet is deflected by the magnetic field) on [FORMULA] and [FORMULA]. Our numerical results indicate that [FORMULA] is a decreasing function of the field angle [FORMULA]. We find a nearly linear dependence of [FORMULA] on the ambient field strength [FORMULA]. Our numerical results are in good qualitative and rough quantitative agreement with an analytical model derived from a two-dimensional consideration of the ram pressure balance governing the motion of the jet head. This model predicts an unrealistically high ambient field strength of [FORMULA]G to deflect a jet of 100 km s-1 (appropriate to stellar jets). Applying our results to L 1221 and HH 110/HH 270 we thus suggest that in these sources the jet/outflow must interact with a relatively strong magnetic field ([FORMULA]G) contained in a dense clump of ambient gas ([FORMULA] cm-3) if deflection is to be caused by magnetic forces. In the case of L 1221 two other possible explanations of the observational data can be given by assuming (i) that only a low speed wind surrounding the driving jet is bent by an ambient field while the outflow-driving jet itself remains straight and invisible due to high obscuration by ambient material, or (ii) that the outflow contains no high speed driving jet at all and can therefore be deflected by a moderate ambient field ([FORMULA]G).

Key words: ISM: individual objects: L 1221 – ISM: individual objects: HH 110/HH 270 – ISM: magnetic fields – ISM: jets and outflows – methods: numerical – Magnetohydrodynamics (MHD)

Present address: Lehr- und Forschungsgebiet für Mechanik, RWTH Aachen, Templergraben 64, D-52062 Aachen, Germany

Send offprint requests to: J.D. Hurka (hurka@lufmech.rwth-aachen.de)

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999

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