Astron. Astrophys. 347, 1055-1068 (1999)

Outflows from magnetic rotators

II. Asymptotic structure and collimation

T. Lery ^1,2, J. Heyvaerts ¹, S. Appl ^1,3 and C.A. Norman <sup>4

1</sup> Observatoire de Strasbourg 11 rue de l'Université, F-67000 Strasbourg, France
² Department of Physics, Queen's University, Kingston, Ontario, K7L 3N6, Canada
³ Institut fuer Angewandte Mathematik, Universitaet Heidelberg, Im Neuenheimer Feld 293, D-69120 Heidelberg, Germany
⁴ Space Telescope Science Institute and Johns Hopkins University, 3700 San Martin Drive, Baltimore, MD 21218, USA

Received 10 August 1998 / Accepted 12 May 1999

Abstract

The asymptotic structure of outflows from rotating magnetized objects confined by a uniform external pressure is calculated. The flow is assumed to be perfect MHD, polytropic, axisymmetric and stationary. The well known associated first integrals together with the confining external pressure, which is taken to be independent of the distance to the source, determine the asymptotic structure. The integrals are provided by solving the flow physics for the base within the framework of the model developed in Paper I (Lery et al. 1998), which assumes conical geometry below the fast mode surface, and ensures the Alfvén regularity condition. Far from the source, the outflow collimate cylindrically. Slow (i.e. with small rotation parameter ) rigid rotators give rise to diffuse electric current distribution in the asymptotic region. They are dominated by gas pressure. Fast rigid rotators have a core-envelope structure in which a current carrying core is surrounded by an essentially current free region where the azimuthal magnetic field dominates. The total asymptotic poloidal current carried away decreases steadily with the external pressure. A sizeable finite current remains present for fast rotators even at exceedingly small, but still finite, pressure.

Key words: Magnetohydrodynamics (MHD) stars: mass-loss stars: pre-main sequence stars: winds, outflows

Send offprint requests to: T. Lery (lery@astro.queensu.ca)

SIMBAD Objects

Contents

• 1. Introduction
• 2. The analytical model
  • 2.1. The jet base
  • 2.2. The intermediate zone
  • 2.3. The asymptotic structure
• 3. Numerical analysis
  • 3.1. Numerical procedure
  • 3.2. Variations of the rotation
  • 3.3. Mass loss rate effects
  • 3.4. Thermal effects
  • 3.5. An example: BP Tau
  • 3.6. Non-constant and Q
• 4. The asymptotic electric current
  • 4.1. Current and pressure balance
    • 4.1.1. Slow rotators
    • 4.1.2. Fast rotators
  • 4.2. Variation of the current across the flow
  • 4.3. Evolution of the current along the flow
  • 4.4. Influence of source properties
  • 4.5. Influence of the external pressure
  • 4.6. Differential rotators
• 5. Comparison between numerical results and a simplified model
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999
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