Wind-driving protostellar accretion discs. II. Numerical method and illustrative solutions

TL;DR

This paper develops and tests a numerical method for modeling wind-driving protostellar accretion discs, confirming theoretical predictions and providing a library of solutions to aid future research and observations.

Contribution

It introduces a numerical approach to solve disc equations in the Hall diffusivity regime and extends solutions to larger scales by matching with global wind models.

Findings

Numerical solutions confirm hydrostatic analysis predictions.

Solutions can be extended to cross the Alfvén surface.

A library of wind solutions is provided for community use.

Abstract

(abridged) We continue our study of weakly ionized protostellar discs that are threaded by a large-scale magnetic field and power a centrifugally driven wind. It has been argued that in several protostellar systems such a wind transports a significant fraction of the angular momentum from at least some part of the disc. We model this case by considering a radially localized disc model in which the matter is well coupled to the field and the wind is the main repository of excess angular momentum. We consider stationary solutions in which magnetic diffusion counters the shearing and advection of the field lines. In Wardle & K\"onigl we analysed the disc structure in the hydrostatic approximation and presented disc/wind solutions for the ambipolar diffusivity regime. In K\"onigl, Salmeron & Wardle (Paper I) we generalized the hydrostatic analysis to the Hall and Ohm diffusivity domains and identified the parameter sub-regimes in which viable solutions occur. In this paper we test these results by deriving numerical solutions (integrated through the sonic critical surface) of the disc equations in the Hall domain. We confirm the predictions of the hydrostatic analysis and demonstrate its usefulness for clarifying the behaviour of the derived solutions. We show that the solutions can be extended to larger scales (so that they also cross the Alfv\'en critical surface) by matching the localized disc solutions to global wind solutions of the type introduced by Blandford & Payne. To facilitate this matching, we construct a library of wind solutions, which is made available to the community. The results presented in Wardle & K\"onigl, Paper I and this work form a comprehensive framework for the study of wind-driving accretion discs in protostellar and other astrophysical environments. This tool could be useful for interpreting observations and for guiding numerical simulations of such systems.