| 其他摘要 | W UMa-type binary is a late-type close binary with both components filling their critical Roche Lobes and sharing a convective common envelope. They follow the famous period-color relation, which means that the shorter period W UMa-type binaries have the lower effective temperature (or later type) of the components. The very short period contact binaries are W UMa-type binary systems consisting of GKM type stars, with periods generally less than 0.3 days. They are ideal laboratories for the study of periodic cutoff and w-type phenomena of contacting binary stars, and are of great significance for the study of the formation and evolution of red dwarf contacting binary stars and the theory of thermal relaxation oscillation of contacting binary stars. In this paper, the samples of very short period (VSP) contact binary with period analysis results at present are collected and collated, and a preliminary statistical analysis is carried out on their contact degree and period variation characteristics, and the formation and evolution of red dwarf contacting binaries and the possible causes of W-type phenomena are discussed through the detailed study of several very short period contact binaries with different spectral types and their related celestial bodies. The main results are as follows:1. By investigating the period variation and contact degree of 64 VSP contact binaries, we found that most of the VSP contact binaries are W-type systems with low contact degree, and the contact degree is mainly concentrated between 0 - 0.25. Some of these systems have increasing orbital period and some have decreasing orbital period, and the number of increasing orbital period and decreasing orbital period is equal, which suggests that the W-type VSP contact binary systems are probably in thermal relaxation oscillation.2. Based on the complete multi-color light curves obtained from observations, we conducted photometric analysis, combined with the stellar atmosphere parameters of LAMOST and parallax information of GAIA, we gave the structural characteristics and absolute physical parameters of very short period close binaries V0627 Hya, V0644Ser and J2128, and found that they were all red dwarf contact binary systems. By analyzing the characteristics of photometric distortion in different bands and orbital period, we found that there may be a low mass third body orbiting around them. Because the evolution time scale and angular momentum loss time scale of red dwarf binary is too long, it is very difficult to form red dwarf binary, these third body are likely to move angular momentum to promote the central binary pair contact, thus becoming one of the reasons for the formation of red dwarf binary.3. The comparative analysis of three complete multi-color light curves spanning six years (2013, 2015 and 2019) of red dwarf contact binary J2128 shows that the light curves change significantly with time, from EW-type to EB-type, and the photometric resolution results also change from A-type to W-type. This variation is best explained by the large area of spot coverage caused by the magnetic activity of the component star. We collected and sorted out the currently discovered contact binary systems that convert between A-type and W-type, and found that their spectral types are all later than F7 and their light curves are all asymmetrical to varying degrees, suggesting that the magnetic activities of stars are likely to be the cause of W-type phenomenon.4. Two G-type VSP contact binaries CY Ari and IK Lyn with different metallicities are compared and analyzed. We found that they are both W-type shallow contact binaries with similar surface effective temperature Teff and gravitational acceleration log(g), and the metallicities [Fe/H] of CY Ari and IK Lyn are 0.173 and -0.79, respectively. The analysis of their orbital period changes shows that their orbital periods are increasing for a long time, and there may be a close White Dwarf third body with a mass of 0.61M⊙ in CY Ari. The high metallicity of CY Ari may come from the material pollution during the formation of the third body.5. The observation and analysis of the VSP eclipsing binary system V443 UMa with EB-type shows that V443 UMa is a close contact binary system with a decreasing orbital period for a long time. V443 UMa currently has a period of 0.2222404 days, and as the orbital period shrinks, it will evolve into a contact binary system, revealing that red dwarf contact binary can also form through the near contact binary channel. |
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