The Circumstellar Material Around Type Ⅰa Supernovae And Their Influence On The Light Curve And Polarization

Type Ⅰa supernovae(SNe Ⅰa)are originated from the thermonuclear explosion of a carbon-oxygen white dwarf whose mass reaches the Chandrasekhar limit.The B-band maximum luminosity and the width of the light curve satisfy the Phillips relationship,so it is widely used as a standard candle for cosmological distance.However,it is not clear how white dwarfs reach the Chandrasekhar limit.The study of the circumstellar material(CSM)will provide a unique perspective for distinguishing different pre-supernovae evolution.Accretion and merging are the two most common process of mass increase in astronomy.The accretion process is usually accompanied by the stellar wind and other outward transfer of materials,and the corresponding white dwarf will explode in an environment where the CSM exists.It is important for a profound understanding of the progenitor evolution and explosion mechanism to systematically study the influence of CSM on the light curve,spectrum and polarization of SNe Ⅰa,and further to limit the physical state of CSM,such as the spatial distribution and optical depth.Based on this premise,the main research content of this paper includes the following parts:In chapter 1,the current observations about SNe Ⅰa and CSM are summarized.In chapter 2,we introduce the radiative transfer process in CSM,and the intensity distribution relating to multiple scattering is numerically solved by the Monte Carlo method.We consider three possible geometric distributions of CSM,including shell,disk,and asymmetric shell.For each spatial distribution,our simulation shows that the CSM parameters(e.g.,optical depth,inner and outer radius of CSM)are degenerate,that is,similar intensity distributions may correspond to different CSM parameter values.Combining the light curve and polarization signals of SNe Ⅰa can well limit the CSM parameter value.In chapter 3,we apply the dust scattering model to high-velocity(HV)SNe Ⅰa.The statistical blue-shifted and the time-varying sodium absorption lines indicate the relation between HV SNe Ⅰa and CSM.Comparing the light curve of the normal-velocity(NV)SNe Ⅰa,HV SNe Ⅰa have a bump in the B band after a few months respective to the maximum light,but it is not obvious in the V band.We attribute this phenomenon to the light echo of dusty CSM at an appropriate distance from HV SNe Ⅰa.Combined with the polarization signal about 300 days after the maximum light,the distance of the CSM around SN 2014J can be limited to about 5 × 1017 cm.In chapter 4,we study the influence of the thermal emission of dusts in CSM on the near-infrared light curve of SNe Ⅰa,and use multi-band light curves(optical and near-infrared)to limit the distance of CSM.We have obtained the light curve data of a number of SNe Ⅰa with good multi-band observations from several supernova surveys and literature.The data of NV SNe Ⅰa are used to synthesize the light curve template,and the dust scattering and thermal emission are used to fit the optical and near-infrared light curve of HV SNe Ⅰa,respectively.The results show that for HV SNe Ⅰa with nearinfrared excess,the distance of CSM is mostly less than 1017 cm.In chapter 5,we investigate the middle-infrared excess of SN 2018evt during its late time.Through fitting the data by newly formed dust model,the CSM model with shell structure and the CSM model with blob structure,we find that the process of forming newly dusts during around+445 days is necessary to fit the middle-infrared data.In chapter 6,we briefly look forward to the theoretical and observational research in the future.