Comparisons of MHD Propeller Model with Observations of Cataclysmic Variable AE Aqr

TL;DR

This paper presents a numerical MHD model of the star AE Aqr, explaining its observational properties, rapid spin-down, and flaring activity through disc-magnetosphere interactions and outflows.

Contribution

The study introduces a detailed axisymmetric MHD simulation of AE Aqr, demonstrating its propeller regime and matching observed phenomena with theoretical predictions.

Findings

Model explains rapid spin-down via angular momentum outflow.

Most accreted matter is ejected in winds, consistent with observations.

Energy in outflows accounts for observed flaring radiation.

Abstract

We have developed a numerical MHD model of the propeller candidate star AE Aqr using axisymmetric magneto-hydrodynamic (MHD) simulations. We suggest that AE Aqr is an intermediate polar-type star, where the magnetic field is relatively weak and an accretion disc may form around the white dwarf. The star is in the propeller regime, and many of its observational properties are determined by the disc-magnetosphere interaction. Comparisons of the characteristics of the observed versus modelled AE Aqr star show that the model can explain many observational properties of AE Aqr. In a representative model, the magnetic field of the star is B\approx 3.3x10^5 G and the time averaged accretion rate in the disc is 5.5\times 10^{16} g/s. Most of this matter is ejected into conically-shaped winds. The numerical model explains the rapid spin-down of AE Aqr through the outflow of angular momentum from the surface of the star to the wind, corona and disc. The energy budget in the outflows, 9x10^{33} erg/s, is sufficient for explaining the observed flaring radiation in different wavebands. The time scale of ejections into the wind matches the short time scale variability in the light curves of AE Aqr.