The Progenitors Of Type Ia Supernovae And The Formation Of Intermediate-mass Binary Pulsars

Type Ia supernovae(SNe Ia)are among the most powerful phenomena in the universe.Owing to the remarkable uniformity of their high luminosity,SNe Ia are successfully used as standard candles to measure cosmological distances.It has been verified that the Universe is expanding at an increasing rate based on the observations of SNe Ia,leading to the discovery of dark energy.Meanwhile,most of the iron in the host galaxy are produced by SN Ia explosions.However,the progenitors of SNe Ia remain unclear,which may affect the accuracy of distance measurement and the reliability of current galaxy chemical evolution models.The most popular progenitor models for SNe Ia are the single-degenerate(SD)model and the double-degenerate(DD)model.There are also some sub-luminous SNe Ia in the observations,which can be explained by the double-detonation model.In addition,intermediate-mass binary pulsars(IMBPs)are composed of a neutron star(NS)and a white dwarf(WD).However,the formation channels of IMBPs are still not fully conformed.In this thesis,we introduced the backgrounds and research status of SNe Ia in details,and reviewed their progenitor models and observational constraints.We also introduced the backgrounds of IMBPs.We have conducted a series of investigations on the progenitors of SNe Ia and the formation of IMBPs.We proposed the WD+heluim(He)subgiant model,and found that this model has a significant contribution to the formation of double massive WDs and the delay time distributions of SNe Ia can be reproduced.We improved the prescription for the mass-transfer of semidetached bi-naries,and found that the parameter space for producing SNe Ia via the symbiotic channel is significantly enlarged,which is useful for solving the contradiction between the low predicted rate and the large number of observed symbiotic systems.We systematically investigated the carbon-oxygen(CO)WD+He-rich WD merging mod-el,and found that this model is a possible path for producing sub-luminous 1991bg like events.We systematically studied the accretion-induced collapse(AIC)model of oxygen-neon(ONe)WD+He star systems,and found that this model can explain the formation of IMBPs.The main results are provided as follows:(1)We proposed the WD+He subgiant model that has significant contribution to the formation of double massive WDs,and found that the observed delay time distributions of SNe Ia can be reproduced.In this model,a CO WD accretes He-rich matter from a He subgiant star,leading to the mass increase of the WD.When the He-shell of the He subgiant is exhausted,the binary becomes a massive double WD system.The merging of the formed double WDs may produce SNe Ia.Previous studies on the DD model have not considered the WD+He subgiant channel,and those studies have deficit with the observed SNe Ia with delay times shorter than1 Gyr and longer than 8 Gyr.We found that the delay time distribution of SNe Ia can be reproduced better after considering the WD+He subgiant channel,and the SN Ia rate from the DD model is consistent with the observed results.It has been suggested that the violent WD merger is more likely to produce SNe Ia based on the DD model.We found that the violent WD merger model may contribute to at most 16%of all SNe Ia,and this model mainly produce SNe Ia in old populations.(2)We improved the prescription for the mass-transfer in semidetached binaries,and systematically investigate the symbiotic model for producing SNe Ia.We found that the initial parameter space for producing SNe Ia via this model is significantly enlarged.In the observations,there are many symbiotic systems,in which some of these systems have massive WDs with masses near to the Chandrasekhar limit(e.g.RS Oph,T Crb).However,the predicted rate of SNe Ia is relatively low.Previous studies usually assumed that the exceeding mass of the RG star would be immedi-ately transferred,leading to a relatively high mass-transfer rate,preventing the WD from increasing its mass to the Chandrasekhar limit.We improved the prescription for mass-transfer process,and obtained the parameter space,rates and delay time distributions of SNe Ia from the symbiotic channel.Compared with previous models,the parameter space and the predicted rates are significantly enlarged.We also found that this model may contribute to SNe Ia in the intermediate and old populations,and the symbiotic systems RS Oph and T CrB will form SN Ia explosions via the symbiotic model.(3)We systematically investigated the CO WD+He-rich WD model,and found that this merging model is a possible pathway for the formation of sub-luminous SN1991bg-like events.He-rich WDs include He WDs and hybrid HeCO WDs,in which a hybrid HeCO WD contains a CO core and a He-rich shell.During the merging process,the He-rich envelope detonates on the surface of the CO WD when it is thick enough.The shock wave into the CO core would trigger a second detonation of the whole CO WD,leading to the formation of sub-luminous SNe Ia.However,there are still very few binary population synthesis studies on the CO WD+He-rich WD model.We systematically studied this merging model,and found that this model may contribute to at most 15%of all SNe Ia,mainly producing SNe Ia in intermediate and old populations.Compared with normal SNe Ia,SN 1991bg-like events are fainter and their light curves decline faster.We also found that the CO WD+He-rich WD merging model can reproduce the observed rates of SN 1991bg-like events,and can explain the delay time distributions of these events,which indicates that this merging model is a possible formation channel for SN 1991bg-like events.(4)We systematically studied the AIC model of ONe WD+He star systems,and found that this model can explain the observed IMBPs with short orbital periods.IMBPs are composed of a NS and a WD,in which the spin periods of NSs are in the range of 10-200 ms and the masses of the WDs are larger than 0.4 M_?.However,the formation of IMBPs is still under debate.Previous studies can only account for part of IMBPs with short orbital periods.According to the AIC model of ONe WD+He star systems,we provided the initial parameter space,the parameter space of formed NS+He star systems after AIC and the eventually formed IMBPs,and found that almost all of the observed IMBPs with short orbital periods can be covered by this model.We also obtained a possible evolutionary path for PSR J0621+1002,and found that the observed parameters of PSR J1802-2124 can be well reproduced.We also speculated that the compact companion of HD 49798 may be a WD but not a NS.