Features of the Accretion in the EX Hydrae System: Results of Numerical Simulation

TL;DR

This study uses 2D numerical simulations to explore the accretion process in the EX Hya system, revealing curtain-like accretion columns and highlighting the limitations of the magnetic field penetration assumption.

Contribution

It introduces a 2D axisymmetric model of accretion in EX Hya and discusses the implications of magnetic field penetration assumptions on accretion curtain thickness.

Findings

Accretion occurs via curtain-like columns that are not closed.

Simulated curtain thickness is inconsistent with observations.

Magnetic shielding by a diamagnetic disk may better explain observed features.

Abstract

A two dimensional numerical model in the axisymmetric approximation that describes the flow structure in the magnetosphere of the white dwarf in the EX Hya system has been developed. Results of simulations show that the accretion in EX Hya proceeds via accretion columns, that are not closed and have curtain-like shapes. The thickness of the accretion curtains depends only weakly on the thickness of the accretion disk. This thickness developed in the simulations does not agree with observations. It is concluded that the main reason for the formation of thick accretion curtains in the used model is the assumption that the magnetic field penetrates fully into the plasma of the disk. An analysis based on simple estimates shows that a diamagnetic disk that fully or partially shields the magnetic field of the star may be a more attractive explanation for the observed features of the accretion in EX Hya.