| 其他摘要 | Hot subdwarf-B stars are helium-core burning objects with extremely thin hydrogen rich envelopes (< 0.02M⊙). Due to the thin hydrogen envelopes of hot subdwarf-B stars, their progenitors must lose the majority of hydrogen envelopes before helium core igniting. However, the theory of single star evolution is difficult to explain what mechanism dominates the loss of so much material in the progenitors of hot subdwarf-B stars. Observations show that nearly half of hot subdwarf-B stars are located in close binary systems, and binary interactions may play an important role in the formation of hot subdwarf-B stars. The stable Roche lobe overflow, common envelope ejection, indicating that double helium white dwarfs merger are the main channels for the formation of hot subdwarf-B stars. However, the fast binary evolution algorithm for calculating stellar evolution in the Yunnan-II evolutionary population synthesis models cannot generate hot subdwarf-B stars through these binary channels normally.Therefore, one of the purposes of this paper is to use the Yunnan-II evolutionary population synthesis models to improve the evolution of hot subdwarf-B stars formed by the stable Roche lobe overflow, common envelope ejection, and double helium white dwarfs merger in the fast binary evolution algorithm. Different metallicities, common envelope efficiency parameters, angular momentum loss factors, mass transfer rates, critical mass ratios, and initial parameters of binary stars all have important impacts on the evolution process and results of binary stars. Thus, the second purpose of this paper is to establish a model for the formation of hot subdwarf-B stars in binary channels using different parameters of the fast binary evolution algorithm, and to study the effects of different parameters on the formation of hot subdwarf-B stars in binary channels. With the development of various observation technologies, more and more hot subdwarf-B stars are being discovered, and some of their parameters (mass, orbital period, etc.) are also being measured more accurately. Accordingly, the third purpose of this paper is to compare the observed samples with various star models to obtain the best model that can explain the observations, which is also the main purpose of this paper. This paper used the fast binary evolution algorithm to provide 42 models with metallicities Z= 0.02 and 42 models with metallicities Z = 0.004 under different parameter conditions. In each model, we calculated the evolution results of 106 binary stars starting from the zero age main sequence, and studied the evolution channels and various parameter effects of binary star formation of hot subdwarf-B stars. By comparing the mass, companion mass, and orbital period of hot subdwarf-B stars observation samples, we found that the mass distribution of hot subdwarf-B stars formed by the stable Roche lobe overflow and common envelope ejection channels in model 17 is between 0.32 M⊙~0.8M⊙, and there is a peak near 0.47M⊙. The mass distribution of hot subdwarf-B stars formed through the double helium white dwarfs merger is between 0.40 ∼ 0.65M⊙, with an average mass of approximately 0.52M⊙. In addition, the common envelope ejection channel in model 17 forms hot subdwarf-B stars with main sequence companion star with orbital periods ranging from 2 hours to 1 day, and hot subdwarf-B stars with white dwarf companion star with orbital periods ranging from 1 hour to 27 days, and the stable Roche lobe overflow channel also produces hot subdwarf-B stars with longer orbital periods. Through comparison, we found that these results are basically consistent with existing theories and can to explain the observed distribution of hot subdwarf-B stars. Therefore, the rapid binary evolution algorithm can be used to realize the evolution of hot subdwarf-B stars formed by binaries, and the model established by different parameters can effectively test the influence of different parameters on the evolution of hot subdwarf-B stars formed by binary stars. In addition, the hot subdwarf-B stars generated by model 17 using the fast binary evolution algorithm will also provide important assistance for the research of evolutionary population synthesis models. |
修改评论