On The Evolution Of White Dwarf Binaries

White Dwarf(WD)binaries belong to one class of compact binary systems.Usually they consist of a white dwarf and a normal star.Most stars evolve into white dwarfs during the evolution(larger ones collapse into neutron stars or black holes).In our Galaxy,about 10 percent of the white dwarfs are in binary systems.Therefore,the systematic study of the white dwarf binaries helps us to understand some important processes in the evolution of binary stars,including mass transfer in the binaries,structure and stability of the accretion disk,Supersoft X-ray Sources(SSSs),Type la Supernovae,Cataclysmic Variables(CVs)and Millisecond Pulsars(MSPs).This thesis is divided into the following four chapters.In Chapter One,in the first part,we mainly introduce the concept of SSSs.Firstly,we introduce the construction of binaries,including the Roche Lobe effective equipotential surface and the basic classification method for binaries.Then we introduce the observational characteristics of SSSs and then We introduce the theoretical model of SSSs including why the SSSs are binaries including white dwarfs,the nuclear burning process of the accreting WD and the conditions which can produce SSSs.At last,We introduce the origin and the evolution of SSSs,respectively.In the second part,we mainly introduce the concept of CVs.First we present the observational characteristics of CVs.which include the classification methods for CVs,the WD mass distributions in CVs and the orbital period distributions of CVs(including the orbital period gap and the orbital period minimum).Then the accretion disk instability is introduced.In the final,we present the evolutionary process of pre-CVs and CVs.For the evolution of CVs,angular momentum loss(AML)dominate the evolution,including systemic AML and consequential AML.In Chapter Two,we present our first work,which is on the WD mass problem of CVs.Recent observations show that WDs in CVs have an average mass significantly higher than isolated WDs and WDs in post-common envelope binaries(PCEBs),which are thought to be the progenitors of CVs.This suggests that either the WDs have grown in mass during the PCEB/CV evolution or the binaries with low-mass WDs are unable to evolve to be CVs.In this work,we calculate the evolution of accreting WD binaries with updated hydrogen accumulation efficiency and angular momentum loss(AML)prescriptions.We show that thermal-timescale mass transfer(TTMT)is not effective in changing the average WD mass distribution.The WD mass discrepancy is most likely related to unstable mass transfer in WD binaries,in which an efficient mechanism of AML is required.In Chapter Three,we introduce the evaporation effect of the newborn Neutron Star(NS)which has experienced post accretion-induced collapse(AIC).AIC is widely accepted to be one of the formation channels for MSPs.Since the MSPs have high spin-down luminosities,they can immediately start to evaporate their companion stars after birth.In this work,we present a detailed investigation on the evolution of the post-AIC binaries,taking into account the effect of evaporation both before and during the Roche-lobe overflow process.We discuss the possible influence of the input parameters including the evaporation efficiency,the initial spin period,and the initial surface magnetic field of the newborn neutron star.We compare the calculated results with the traditional low-mass X-ray binary evolution and suggest that they may reproduce at least part of the observed redbacks and black widows in the companion mass-orbital period plane depending on the mechanisms of AML associated with evaporation.In Chapter Four,we summary our work and present some expectation for the future work.