| 其他摘要 | Early-type contact binary stars are a type of binary system characterized by having O, B, or A spectral type sub-stars that fill their respective Roche lobes and share a common radiative envelope, exhibiting strong mutual interactions. Due to limited observational samples and detailed analyses, the formation, evolution, and physical processes related to mass transfer in these systems remain poorly understood. The Small Magellanic Cloud (SMC), a nearby galaxy with lower metallicity compared to the Milky Way, has been a focus of the Optical Gravitational Lensing Experiment (OGLE), which has discovered a large number of eclipsing binary stars in the SMC. In this study, we systematically analyze and perform orbit solutions and orbital period analyses of early-type contact binary stars in the SMC using observational data from OGLE-IV and previous surveys. We aim to derive their fundamental physical parameters and investigate the causes of their orbital period variations. By comparing the statistical data of early-type contact binary stars in the SMC with those in the Milky Way, we explore the influence of different galactic environments on early-type contact binary stars.We selected those contact binaries from the OGLE-IV data that had V-I color index less than -0.07 mag, period less than 1 day, and eclipse depth greater than 0.15 mag. We also excluded systems with highly scattered light curves, resulting in a final sample of 17 targets. By combining the observations from the earlier phases of OGLE, we obtained the time span of up to 20 years for these sources and analyzed their O-C diagrams to determine their mass transfer, third body and other related parameters. Furthermore, we used the W-D program to analyze the OGLE-IV photometric data for these sources, which allowed us to derive their fundamental physical parameters. In order to provide a basis for comparison, we also carried out a detailed analysis of the high-mass binaries in the Milky Way. The specific results of our study are as follows.1. The orbital period analysis of the three high-mass binary stars in the Milky Way, HI Mon, TU Mus, and AI Cep, has led to new discoveries. In the case of HI Mon, a periodic oscillation in the orbital period was observed for the first time, suggesting the presence of a companion object. Further analysis of the orbital period of TU Mus confirmed previous findings, where the O-C curve exhibited dual periodic variations, indicating the presence of a quadruple system consisting of a visual companion and an invisible companion, causing the periodic changes in the orbital period. The orbital period analysis of AI Cep revealed an upward-opening parabolic trend in the O-C curve, indicating a long-term increase in its period, suggesting mass transfer from a lower-mass companion to a higher-mass companion.2. The study revealed that out of the 17 systems analyzed, 7 eclipsing binary stars exhibited periodic oscillations in their O-C curves, indicating periodic increase or decrease in their orbital periods. These findings confirm that these variations are caused by the light-time orbital effects. By utilizing the Wilson-Devinney (W-D) program to analyze the I-band light curves obtained from OGLE observations, 6 of these systems were examined. The results demonstrated the presence of third bodies in these systems with orbital periods ranging from 6.41 to 24.65 years and minimum masses ranging from 0.31 M_sun to 4.11 M_sun. Among these six systems, four exhibited negative dP/dt values, indicating a continuous decrease in their periods. The analysis of the contact degrees from the W-D results revealed three deep contact binary systems, one moderate contact binary system, and two shallow contact binary systems. The shallow contact binary systems are likely newly formed due to rapid mass transfer. The results indicate that the proportion of multiple-star systems (binary systems with a third body) in early-type contact binary systems in the Magellanic Clouds is much higher (14%) compared to the overall proportion of multiple-star systems in the Magellanic Clouds and significantly higher than that in the Galactic stellar systems observed by the Kepler satellite (1/12).3. OGLE-SMC-ECL-2063 is a short-period early-type binary with a period of 0.6317643d in the SMC, we observed it using the 1m telescope at the South African Astronomical Observatory and obtained data for two nights. We use the Wilson-Devinney code to analyze its light curves. The result shows that OGLE-SMC-ECL-2063 is an overcontact binary with a high mass ratio of 0.900 and a fill-out factor of 35.9%. The O-C curves that the period of OGLE-SMC-ECL-2063 shows a long-term increase with a cyclic oscillation of amplitude A = 0.00503d and period P_3 = 14.80yr. All evidence above indicates that OGLE-SMC-ECL-2063 is in the Case A mass transfer evolutionary state. The mass transfer rate dM2/dt=-5.67 x 10^-7M_sun/yr is derived and used to explain the continuous period increase. For both components of OGLE-SMC-ECL-2063 are early-type stars, the existence of a third body may be the reason for the cyclic change in period. The mass of the third body is derived to be no less than 0.70 M_sun and the orbital separation to be no more than 13.22 AU. Combining the result of light curve analysis, the third body tends to be a low-mass late-type star. Such high mass-ratio binaries play an important role in the evolution of early-type binaries. 4. Among the 17 candidate objects selected in the Small Magellanic Cloud (SMC), 10 contact binary stars show no significant periodic variations in their orbital periods based on the current observational data. Through the analysis of the O-C curves, it was found that four contact binary stars exhibit a long-term decrease in their orbital periods, while one contact binary star shows a long-term increase in its orbital period. Among them, the orbital period variations of three contact binary stars are primarily caused by angular momentum loss, while the remaining ones are mainly due to mass transfer. By analyzing their I-band light curves using the W-D program, it was discovered that six contact binary stars are in a deep contact state, three are in a shallow contact state, and one is in a moderate contact state. The temperature ratios of all contact binary stars are close to 1. Finally, combining the analysis of the light curves and period variations of the 17 sources, including the seven high-mass contact binary stars with third bodies, the evolution of high-mass binary stars was explored. The results revealed that most high-mass contact binary stars are likely formed through a rapid mass transfer phase.5. In the study of high-mass contact binary stars in the Small Magellanic Cloud (SMC), some binary systems in special evolutionary stages have been identified. Firstly, the W-D fitting results reveal that three high-mass contact binary stars have mass ratios very close to 1, a configuration often referred to as twin binary stars. Secondly, more than half of the targeted contact binary stars in our research exhibit contact degrees exceeding 50%. Notably, OGLE-SMC-ECL-1987 stands out with a contact degree exceeding 90%, making it of significant importance for future investigations. |
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