| 其他摘要 | Astrometric microlensing events provide us unique opportunities to obtain direct mass determinations of isolated stars. It can detect compact objects like isolated neutron stars and black holes and has an important role on astrophysical studies. Precisely predicting when and where the events will occur from the huge amounts of Gaia data using astrometric methods is a key tool to successfully detect the events for space and ground large telescopes. The thesis includes the main works as follow:1, In the face of massive Gaia data, this thesis develops a secondary pairing method for the initial pairing of lens stars-background stars. While ensuring the completeness of the predicted events, the initial pairing star pairs are minimized as much as possible to reduce subsequent computational complexity. The reliability of this method was verified through comparative experiments.2, The thesis deduces the relationship between the daily variation of the observed signal of the astrometric microlensing events and the separation, the proper motions, the parallax and the flux ratio. It is concluded that more than 98 % of the predicted event have the diurnal variation of the astrometric signals far less than 100𝜇as/yr, and then a simple and fast method for calculating the closest approach of the star pair to obtain the maximum observation signal is proposed. Only a small number of data points are calculated to obtain results that are consistent with other researchers without any complex algorithm.3, The thesis has carried out a search for possible astrometric microlensing events in Gaia DR3.According to the median accuracy of Gaia satellite, the search target is these events with bright image position offsets greater than 0.1mas and occurs between 2010 and 2070. In the Chapter 5,the potential lens stars are selected from three types of stars, e.g., high-proper-motion stars, nearby stars and high-mass stars. In addition to the traditional mass-light relationship, the thesis also uses Gaia DR3's "Astrophysical Parameter Table" and white dwarf catalog tables to estimate the mass of potential lensing stars. For star pairs with the astrometric microlensing signals more than 0.1mas, in addition to using the "ruwe" parameter of Gaia DR3, multiple methods such as "astrometric fidelity" parameter, cross matching with Gaia DR2 and 12 external databases are also used to exclude spurious astrometric solutions, binary stars or co-moving stars, making the prediction results to be complete and reliable. Finally, 4500 events caused by 3558 lens stars are found, of which 1664 are new prediction events. In addition, it was found that 293 lens stars can cause two or more prediction events. Surprisingly, there are five lens stars to cause more than 50 events. In the future, by observing these prediction events, the measurement accuracy of lens star mass can be greatly improved. The thesis discuss two of these lens stars and their corresponding events. In addition, the thesis also find 348 predicted events with maximum astrometric microlensing signals greater than 0.5mas and minimum angular distance between stars greater than 105mas, including 97 events with maximum astrometric microlensing signals even greater than 1mas.This is very beneficial for following-up observation.4, Based on the results of Chapter 5,the thesis also uses these stars with 3M⊙ |
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