| 其他摘要 | Type Ia supernovae (SNe Ia) play an important role in cosmology and the chemical evolution of galaxies. However, their progenitor systems and their explosion mechanisms are still unclear. There are sub-classes of SNe Ia. Type Iax SNe (SNe Iax) are one of the most common and important sub-classes of SNe Ia, which contribute around 1/3 of the total SN Ia rates. Recent studies suggest that SNe Iax may be produced from weak deflagration explosions of Chandrasekhar-mass white dwarfs (WDs) in binary systems with a helium (He) star donor. In this thesis, we have investigated the details of ejecta-companion interaction by performing three-dimensional (3D) hydrodynamical simulations with the smoothed particle hydrodynamics (SPH) method under an assumption of that SNe Iax are generally caused by the above mentioned progenitor model and explosion model. Furthermore, we have followed the long-term evolution of surviving He-star companions of SNe Iax by performing one-dimensional (1D) stellar evolution calculations. The main goal of this thesis is to answer the following questions: (1) What are the consequences of the SN Ia ejecta-companion interaction? (2) What are the post-impact observational signatures of a surviving He-star companion in SNe Iax? Our main results and conclusions can be summarized as follows: (1) By investigating the details of SN ejecta-companion interaction by performing 3D SPH simulations, we find that a small amount of He mass (0.004–0.007 M⊙) is stripped off from the companion surface during the ejecta-companion interaction. The stripped companion material moves with a typical speed of 600–700 km s-1, which is slower than the typical velocity of SN ejecta of 7,000 km s-1 by one order of magnitude. Therefore, one can predict that most of the stripped companion material will be surrounded by SN ejecta as time goes by. This suggests that the He lines caused by the stripped He material can only be visible at late-time phases as the photosphere moves inward from outside of the ejecta to reach the inner region of stripped material. In observations, no He lines have been detected in late-time spectra of SNe Iax yet, which gives an observational upper-limit on the stripped He masses of 0.002–0.1 M⊙. Our work provides an explanation for the non-detection of He-lines in late-time spectra of SNe Iax because that the amount of stripped He masses in our models is very close to (or lower than) the observational upper-limit. (2) By mapping the surviving He-star companion models computed from our 3D impact simulations SNe Iax, we have followed the post-impact evolution of these surviving He-star companions by performing 1D stellar evolution calculations with MESA. We find that the shock heating during the ejecta-companion interaction causes an energy deposition into the He-star companion, which leads to a rapid increase of its luminosity after the impact. About one year after the explosion, the star reaches a peak luminosity of 104 L⊙ and has an effective temperature of 70,000 K, leading to that it appears to be blue and luminous. Subsequently, the surviving He-star companion star contracts and returns to thermal equilibrium state at about 104 yr after the explosion due to the release of gravitational energy, and it becomes a sdO-like star. Since then, the star follows an almost identical evolutionary track of a regular star with the same mass but withoutundergoing the ejecta-donor interaction. (3) Assuming the same progenitor and explosion models for SNe Iax, we extend our previous 3D impact simulations by taking the orbital and spin velocities of the progenitor system into account to investigate their effects on the results of ejecta-companion interaction and post-impact evolution of a surviving He-star companion. We find that the inclusion of orbital and spin velocities of the progenitor system does not significantly affect the total stripped masses and the kick velocity received by the companion star during the interaction. We also find that about 2% of initial angular momentum of the companion star is lost because of mass-stripping during the interaction. In addition, the companion star significantly puffs up due to the shock heating. As a consequence, the surface rotational velocity of the companion star drops to ∼ 180 km s-1 at the end of our impact simulation from its pre-explosion value of ∼ 300 km s-1. The surface rotational velocity of the surviving He-star companion keeps decreasing as it expands, and it reaches the minimum value of ∼ 100 km s-1 when the star expands to a maximum radius at about a few years after the impact. Since then, the star starts to shrink as the deposited energy has radiated away, leading to that the surviving He-star companion spins up again. This peculiar rotation-switching feature would be useful for the identification of surviving He-star companions of SNe Iax in future observations. To summarize, our works provide an explanation for the non-detection of He lines in late-time spectra of SNe Iax. In addition, we provide the theoretical predictions on the post-impact observational characteristics of surviving helium companions of SNe Iax, which will be useful for the identification of surviving He-star companions of SNe Iax in the nearby supernova remnant by future observations. By comparing our results with the observations of SNe Iax, one could place constraints on the progenitor models and explosion mechanisms of SNe Iax and thus further gain a better understanding of SNe Ia. |
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