Dead zones in protostellar discs: the case of jet emitting discs

¹ Dept. of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK e-mail: celine.combet@astro.le.ac.uk
² Laboratoire d'Astrophysique de Grenoble, UJF/CNRS, BP 53, 38041 Grenoble Cedex 9, France
³ Laboratoire APC, Université Paris Diderot, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France

Received: 31 March 2010
Accepted: 22 June 2010

Abstract

Context. Among the many aspects related to planet formation and migration, dead zones are of particular importance as they may influence both processes. The ionisation level in the disc is the key element in determining the existence and the location of the dead zone. This has been studied either within the standard accretion disc (SAD) framework or using parametrized discs.

Aims. In this paper, we extend this study to the case of jet emitting discs (JED), the structure of which strongly differ from SADs because of the new energy balance and angular-momentum extraction imposed by the jets.

Methods. We make use of the (r, z) density distributions provided by self-similar accretion-ejection models, along with the JED thermal structure derived in a previous paper, to create maps of the ionisation structure of JEDs. We compare the ionisation rates we obtain to the critical value required to trigger the magneto-rotational instability.

Results. It is found that JEDs have a much higher ionisation degree than SADs, which renders the presence of a dead zone in these discs very unlikely.

Conclusions. As JEDs are believed to occupy the inner regions of accretion discs, the extension of the dead zones published in the literature should be reconsidered for systems in which a jet is present. Moreover, since JEDs require large-scale magnetic fields close to equipartition, our findings again raise the question of magnetic field advection in circumstellar accretion discs.