The Surviving Companion Stars In Type Ia Supernovae Remnants

Type Ia supernovae(SNe Ia)are used as good cosmological distance indicators and to measure the cosmological parameters,which leads to the discovery of the accelerated expansion of the universe,and then the existence of dark energy.This is a great discovery,not only in astronomy,but also in physics.However,the exact nature of the progenitors of SNe Ia is still unclear.This might affect the reliability of the results of the current cosmological model and galactic chemical evolution model.SNe Ia are widely accepted to arise from thermonuclear explosion of carbon-oxygen white dwarfs(CO WDs)in close binaries.At present,the favoured progenitor models are the singledegenerate(SD)model and the double-degenerate(DD)model.One of the obvious difference between the SD model and the DD model is that the SD model predicts that the companion star can survive from the explosion and show peculiar properties.Therefore searching for the surviving companions in type Ia supernova remnants(SNR)is a potential method to distinguish and to verify the SD and the DD models.Kepler's SN(SN 1604)is one of the only four known historical Galactic type Ia supernova events.Chandra X-ray Observation suggests that the progenitor is most likely to be a WD+AGB system,but the surviving companion has not been found in SN 1604 remnant(Kepler's SNR).One possible explanation is from the spin-up/spin-down model,in which the WD may increase its mass continuously when its mass exceeds the Chandrasekhar mass limit for rapidly rotating WD.The explosion of the WD is significantly delayed and the companion has evolved to be too dim to be detected for a long spin-down timescale.The delayed timescale(i.e.the spin-down timescale)is defined as the time between the end of the mass growth of the WD and the explosion.At present,however,the spin-down time is quite uncertain,but almost certainly exhibits a large range,from < 106 years to > 109 years.Meng& Podsiadlowski(2013)constrained spin-down timescale empirically and obtained an upper limit of a few times 107 yr,which is long enough to erase many signatures thought to be integral parts of SD model,while may be ignorable compared with the delay time of SNe Ia.Therefore,we plan to verify whether the explanation may explain the non-detection result of the Kepler's companion by carrying out binary evolution calculations in detail.In this thesis,we use the Eggleton's stellar evolution code(Eggleton 1971,1972,1973)to study the binary evolution of WD+red giant(RG)star.We assume that for the rapidly rotating WD,the WD can continuously increase its mass when its mass exceeds the Chandrasekhar mass limit(MCh= 1.378M?)until the mass-transfer rate decreases to be lower than a critical masstransfer rate.After the WD stops growing its mass,we obtain essential properties(e.g.the masses,the effective temperatures,the luminosities and the orbital velocities)of the companion stars for different spin-down timescales(e.g.104 yr,105yr,......,109yr).In Chapter 1,we introduced the definition and classification of supernovae,the research status of SNe Ia and the content of this work.We introduced the observational properties(light curve,spectra and so on),progenitor models(SD and DD models)and explosion models of SNe Ia in detail in Chapter 2.Spin-up/spin-down model,the methods used in our work are presented in Chapter3.Finally,we presented our main work of this thesis in detail.The main results of this work are shown as follows:(1)The final masses of WDs range from 1.378M?to 2.707M?,and the companion stars will become CO or He WDs if the spin-down timescale is long enough.(2)If the spin-down time is less than 106 yr,companion stars would be very bright and can easily be observed;but if the spin-down time is ? 107 yr,the luminosities of these surviving companions would be lower than the detection limit.This time scale is consistent with the estimation in Meng & Podsiadlowski(2013).Hence,the surviving companions are difficult to be detected.This is a possible explanation for that no expected surviving companion has been found in Kepler's SNR.Our simulation provides a guidance for the search of the surviving companion stars in SNRs,and the fact that no surviving companion was found in Kepler's SNR may not be the definite evidence disfavoring the SD origin.