| 其他摘要 | Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common envelope. Most of them are believed to be formed mainly from the detached systems through near contact binaries. Once established, these systems evolve toward lower mass ratios via processes such as mass transfer, magnetic braking, and thermal relaxation oscillations. As they approach a critical threshold—known as qmin—they may undergo merging due to tidal Darwin instability. Therefore, investigating low-mass ratio contact binaries is crucial for understanding the evolutionary trajectory of these systems, particularly in their final stages.Utilizing high-precision photometric survey data, such as those provided by the Transiting Exoplanet Survey Satellite (TESS), in conjunction with spectroscopic data and multicolor photometric observations from the ground-based telescopes, we have investigated a group of the close binaries show EW-type light variation, and detected some low mass-ratio contact binaries. Through detailed analysis of these systems, we have derived their physical properties, contributing to our understanding of their characteristics. By integrating these findings with parameters from all known low mass-ratio contact binaries found in the literature, we provide some statistics results about this unique subset of stellar pairs. The main research results of this thesis are as follows: 1. We found three low mass-ratio contact binaries (HV Aqr, MW Pav and TIC 321576458) with filling factor higher than 50%. Among them, HV Aqr has the mass ratio of 0.159 and the contact degree of 56\%, its orbital period is decreasing at the rate of -1.29 × 10-7 days/yr. With the period decrease, the inner and outer critical Roche lobes will shrink, and the degree of overcontact will increase. HV Aqr may evolve from the present low mass ratio and deep-contact binary into a single rapid-rotation star when its surface close to the outer critical Roche lobe. MW Pav has the mass ratio of 0.154 and the contact degree of 71%, its orbital period is increasing at the rate of 1.831 ×10-7 days/yr. such a high degree of overcontact configuration and the long-term period increase suggest that MW Pav may merger into a rapidly rotating single star after its orbital angular momentum becomes less than three times the total spin angular momentum.2. We found three low mass-ratio contact binaries (V458 Mon, V1068 Her and TIC 159102550) at the shallow contact phase. The filling factors and mass ratios are 14%, 21%, 29% and 0.266, 0.211, 0.183 for V1068 Her, TIC 159102550 and V458 Mon respectively. Among them, V1068 Her is the new formed contact binaries with larger temperatures’ difference between the two components and showing EB-type light variation, while TIC 159102550 and V458 Mon trend to have EW-type light variation with similar temperatures of the two stars. The period of both V1068 Her and V458 Mon are increasing, which may indicate that they are under the thermal relaxation oscillations.3. With DASCH database, we efficiently extended the observations of V458 Mon and constructed the O-C curves spanning more than 100 years to investigate the behavior of its orbital period. The results show a reasonable cyclic oscillation with amplitude of 0.139 days and a period of 99.57 year. Assuming this oscillation is results of a third body orbiting around the central binary, the minimum mass of this putative third body is estimated to be 3.1 solar masses, positioned at a separation of approximately 59.59 AU. However, the third light of this system is unseen, implying that V458 Mon may be an important tertiary candidate with compact object. 4. We have collected absolute parameters of 119 low mass-ratio contact binaries. Our analysis of these data indicates that the primary stars are little or un-evolved and secondary ones have evolved out of main sequence zone. Notably, extremely low mass-ratio (q<0.1) contact binaries have more evolved secondary stars. All of the low mass-ratio contact binaries have undergone the mass-ratio inversion process. There appears to be no correlation between the filling-factor and mass-ratio, filling-factor and binary separation, filling factor and spin-orbital angular momentum ratio, period and mass-ratio. The relation between filling-factor and temperature difference between the two components of binaries is also presented. The relationship between mass ratio and spin and orbital angular momentum ratio has been updated and proposed a new qmin = 0.0394 base on these samples. |
修改评论