Hot Spots Drift in Synchronous and Asynchronous Polars: Results of Three-Dimensional Numerical Simulation

Dmitry Bisikalo,Andrey Zhilkin,Andrey Sobolev

doi:10.3390/galaxies9040110

Abstract

In this paper, the characteristics of hot spots on an accretor surface are investigated for two types of polars: the eclipsing synchronous polar V808 Aur and the non-eclipsing asynchronous polar CD Ind in configuration of an offset and non-offset magnetic dipole. The drift of hot spots is analyzed based on the results of numerical calculations and maps of the temperature distribution over the accretor surface. It is shown that a noticeable displacement of the spots is determined by the ratio of ballistic and magnetic parts of the jet trajectory. In the synchronous polar, the dominant influence on the drift of hot spots is exerted by variations in the mass transfer rate, which entail a change in the ballistic part of the trajectory. It was found that when the mass transfer rate changes within the range of 10−10M⊙/year to 10−7M⊙/year, the displacement of the hot spot in latitude and longitude can reach 30∘. In the asynchronous polar, a change in the position of hot spots is mainly defined by the properties of the white dwarf magnetosphere, and the displacement of hot spots in latitude and longitude can reach 20∘.

Highlights

Polars [1] are close binary stars; their optical and infrared radiation is characterized by a significant degree of polarization that is reflected in their name
Parameters of hot spots movement on the accretor surface are investigated for two types of polars—synchronous and asynchronous
It was assumed that a prototype of a synchronous polar is the eclipsed V808 Aur system, and that of a non-eclipsed asynchronous polar is the CD Ind system

Summary

Introduction

Polars [1] are close binary stars; their optical and infrared radiation is characterized by a significant degree of polarization that is reflected in their name. In the case of a synchronous polar and under the assumption of a dipole configuration of the magnetic field in which the center of the dipole coincides with the center of a white dwarf (a non-offset dipole), the position of a hot spot is uniquely determined by the mass transfer rate. In this case, both the latitude and longitude of the energy release zones will vary since they are located symmetrically relative to the orbital plane of a binary system. The main inferences of the paper are briefly discussed

Numerical Model

Asynchronous Polar

Conclusions