Angular momentum transport through magnetic accretion curtains inside disrupted discs

TL;DR

This paper investigates the structure and angular momentum transport in magnetically disrupted accretion curtains around stars, revealing how magnetic fields influence flow dynamics and stellar torque.

Contribution

It provides a detailed analysis of accretion curtain flows, showing magnetic channeling and the feedback of angular momentum into the disc, which affects stellar accretion torque.

Findings

Magnetically channeled, sub-Alfvenic flow is consistent with magnetic field matching.

Some angular momentum is fed back into the disc, reducing stellar torque.

A critical rotation rate exists where the sonic point merges with the curtain base.

Abstract

The structure of accretion curtain flows arising from magnetically disrupted discs is considered. It is shown that a sub-Alfvenic, magnetically channelled flow is consistent with matching the magnetic field across the curtain base. It is shown that some angular momentum is necessarily fed back into the disc, and this reduces the accretion torque acting on the star. The sonic point coordinates are found and a critical rotation rate results below which the sonic point merges with the curtain flow base so, for such stellar rotation rates, little or no thermal assistance is required for material to make the transition to a supersonic flow.