Deflection of stellar jets by ambient magnetic fields

Details Deflection of stellar jets by ambient magnetic fields Deflection of stellar jets by ambient magnetic fields

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...343..558h&link_type=abstract

Astronomy and Astrophysics, v.343, p.558-570 (1999)

Astronomy and Astrophysics

Astrophysics

15

Ism: Individual Objects: L 1221, Ism: Individual Objects: Hh 110/Hh 270, Ism: Magnetic Fields, Ism: Jets And Outflows, Methods: Numerical, Magnetohydrodynamics (Mhd)

Scientific paper

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 vj (in the range 2 to 40 km s(-1) ), the ambient magnetic field strength Ba (50, 100 mu G), and the angle alpha (10degr to 70degr ) between the initial jet velocity and the ambient field to find the dependence of the critical velocity v_cr (up to which a jet is deflected by the magnetic field) on Ba and alpha . Our numerical results indicate that v_cr is a decreasing function of the field angle alpha . We find a nearly linear dependence of v_cr on the ambient field strength Ba. 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 ~ 1000 mu 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 (>= 100 mu G) contained in a dense clump of ambient gas (n >= 10(4) 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 (<~ 200 mu G).

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