| 其他摘要 | A binary system can be simply defined as one containing two stars (also called component stars) that describe closed orbits around their common center of gravity, under the influence of their mutual gravitation. In recent decades, astronomers have discovered more and more distant companion objects (viz. the third and fourth body, etc.) in close binary systems, such system, consisting of three to ten stars that get together under the action of mutual gravitation, is so-called multiple star system. According to the number of member stars, it is called triple system stars, quadruple system stars, and so on. The study and search of companion stars in close binary systems can not only play an important role in the origin and evolution of close binaries, but also has significant meaning on discovery of some special objects, which has recently become an important field of the study of stellar physics! In view of this, a series of research work on companion stars in close binary systems were made in the present doctoral thesis. For the first time，explore the most probable physical mechanism of cyclic period changes in close binary via systemic statistics and analysis of orbital period changes. At the same time, combining small and medium sized telescopes at home and abroad, eleven close binary samples were observed and analyzed in this paper. A series of results are obtained as follows: 1. Starting from the statistical analysis of orbital period changes in close binary system, we find there is no relativity between orbital period changes and the spectral type of the secondary component，which does not support the conclusion derived by American astrophysicist Hall more than 20 years ago. It is indicated that the light travel time effect (LTTE) caused by the third body is the most probable physical explanation of the cyclic period changes in close binaries. 2. We find stellar candidate black holes in the universe, which are the third bodies moving around binary stars. By analyzing the orbital periods of V Pup, WW Dra and WY Per, we find that an unseen companion star exists with these binaries, and the lowest masses of them are 10.4Msun, 6.55Msun and 2.55Msun, respectively. It is suggested that these companion objects are very likely stellar candidate black holes. The discovery of these wide black hole companion stars around close binary systems, could provide the necessary restrictions to the evolution of massive single stars and the formation theory of single black holes. 3. We find the companion stars of early-type close binary AD And, and overcontact binaries V899 Her and VZ Lib are close binaries, respectively. It is indicated that these systems are quadruple systems containing two close binaries; At the same time, we analyze the orbital period changes of the quadruple system HT Vir, which is composed of two binaries. Cyclic period changes in orbital period is found for the first time, and the cause of the cyclic period changes is explored. Additionally, two periodic oscillations in the (O-C) diagrams of early-type binary ZZ Cas and Algol-type binary RW Leo are found by us, suggesting they are also multiple star systems. 4. We find a giant extrasolar planet in orbit around magnetic-braking hibernating cataclysmic variable QS Vir and the eclipsing polar DP Leo, respectively. With an orbital period of about 3.618h, QS Vir containing a white dwarf primary and a red dwarf, we find that the third body is a giant planet with a mass of 6.4MJupiter at a distance of 4.2 astronomical units (AU) from the binary, via the analysis of its orbital period; With a short orbital period of 1.4967h, DP Leo is a strongly magnetic cataclysmic binary. Combing the new observational data by using 2.4-m telescope at Yunnan Observatory and those compiled from literature, we analyze it. It is found that the third body is a giant extrasolar planet with a mass of 6.39MJupiter at a distance of 8.6 astronomical units (AU) from the binary. |
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