Centrifugally driven winds from protostellar accretion discs – I. Formulation and initial results

Abstract

Protostellar discs play an important role in star formation, acting as the primary mass reservoir for accretion onto young stars and regulating the extent to which angular momentum and gas is released back into stellar nurseries through the launching of powerful disc winds. In this study, we explore how disc structure relates to the properties of the wind-launching region, mapping out the regions of protostellar discs where wind launching could be viable. We combine a series of 1.5D semi-analytic, steady-state, vertical disc-wind solutions into a radially extended 1+1.5D model, incorporating all three diffusion mechanisms (Ohm, Hall and ambipolar). We observe that the majority of mass outflow via disc winds occurs over a radial width of a fraction of an astronomical unit, with outflow rates attenuating rapidly on either side. We also find that the mass accretion rate, magnetic field strength and surface density profile each have significant effects on both the location of the wind-launching region and the ejection/accretion ratio $\dot{M}_{\rm out}/\dot{M}_{\rm in}$. Increasing either the accretion rate or the magnetic field strength corresponds to a shift of the wind-launching region to smaller radii and a decrease in $\dot{M}_{\rm out}/\dot{M}_{\rm in}$, while increasing the surface density corresponds to launching regions at larger radii with increased $\dot{M}_{\rm out}/\dot{M}_{\rm in}$. Finally, we discover a class of disc winds containing an ineffective launching configuration at intermediate radii, leading to two radially separated regions of wind launching and diminished $\dot{M}_{\rm out}/\dot{M}_{\rm in}$. We find that the wind locations and ejection/accretion ratio are consistent with current observational and theoretical estimates.