| 其他摘要 | Contact binaries are a kind of binary system whose components are exactly over their Roche lobes and share a common envelope. Due to the strong interaction between the sub-stars, such as mass transfer, the evolution process of the contact binaries has become extremely complicated. Thus, the formation and evolution of contact binaries are still open issues. Thanks to the development of the sky survey, a series of large sample statistical studies can now be carried out on contact binaries. However, these studies are mainly statistical studies of sky survey data such as period and temperature, lacking some statistical research on the internal physical parameters (such as mass ratio, orbital inclination, fill-out factor, etc.) of the contact binaries. Moreover, there are hundreds of high-precision eclipsing binaries with EW-type light curves in the Kepler sky area. And the period and temperature distributions of these samples are consistent with the distributions of more than 5000 EW-type eclipsing binaries observed by LAMOST as of November 2016. Therefore, the statistics of the internal physical parameters of the Kepler small-area contact binaries are somewhat representative of the situation of contact binaries throughout the sky. Meanwhile, the members of an open cluster have the same age, metal abundance, interstellar extinction conditions and the distance. The parameters of the open cluster can well limit the relevant parameters of its members, and to check the reliability of the results of statistical studies of contact binaries from the side. On the other hand, the cluster parameters can constrain the age information of the contact binaries; the dense field environment of the clusters can examine the influence of the third body on the evolution of the contact binaries. Therefore, there are good significances to study the contact binaries in the open clusters.We used the 2015 version Wilson–Devinney program to analyse more than 400 Kepler eclipsing binaries with EW-type light curves. At the same time, the membership identification, physical parameters analysis, and evolutionary state study are carried out for the contact binaries within the tidal radius of two open clusters (NGC 6811 and NGC 6819) in the Kepler sky area.For the statistical research part, a statistical work on Kepler contact binaries was carried out based on the Kepler and Gaia DR2 databases. We have presented the physical parameters (p, T, q, i, f) of 380 Kepler contact binaries based on the Wilson-Devinney program. We also have presented the absolute physical parameters (M1, M2, L1, L2, R1, R2) of 309 Kepler contact binaries based on the photometric solutions and the parallaxes from Gaia DR2. We carried out a statistical study of the obtained physical parameters of the contact binaries, expecting to reveal possible evolutionary connections between the parameters. The main results and conclusions are as follows:1. Based on their periods around 0.2 ~ 1 d and the amplitudes greater than 5%, our samples finally consist of 380 Kepler contact binaries. It has been classified into two subtypes which composed of 160 A-type and 220 W-type contact binaries. The period and temperature distributions of Kepler contact binaries peak around 0.30 d and 5500 K, respectively. This is consistent with the LAMOST observations, indicating that there is no serious selection effect in our sample.2. The mass ratio and fill-out factor distributions show that the mass ratios of contact binaries are concentrated in the range of 0.15-0.55 and the contact binaries generally have shallow fill-out factor, the proportion of contact binaries with fill-out factor less than 30% is around 70%. This should reflect the overall evolutionary distribution of the current contact binaries, and supports the evolutionary view that contact binaries evolve from short-period detached binaries and eventually merge into single star systems.3. The correlation between orbital period and temperature shows a good correlation, it is actually the well-known period-color relationship. It also shows that the long-period (P > 0.5 days) A-type contact binaries are more than W-type ones which may suggest that A-type contact binaries may be less evolved.4. The M-R diagram shows that there is a same linear relationship between the primary and secondary stars while the primary stars are located almost on the ZAMS line, this may be related to the nuclear reaction of the low-mass secondary star. This may be due to energy transfer, which increased the internal temperature of the low-mass secondary star, and the nuclear reaction changed from the pp chains to the CNO cycles.In order to study the contact binaries in the open clusters observed by the Kepler mission, based on the photometric data from the Kepler Eclipsing Binary Catalogue maintained by Villanova University, and combined with the spectral data observed by the 2.16 m telescope at the Xinglong station of National Astronomical Observatories, Chinese Academy of Sciences (NAOC), we analyzed the EW type contact binaries within the tidal radius of NGC 6811 and NGC 6819. At the same time, we estimated the absolute physical parameters of these contact binary systems by using their photometric solutions and the parallaxes data from Gaia DR2 or the period-color-magnitude relationship of the contact binaries. Our main results and conclusions are as follows:1. In the open cluster NGC 6811, we found five EW type binaries, four of them (KIC 9470175, KIC 9533706, KIC 9776718 and KIC 9957411) have a mass ratio less than 0.25; KIC 9532591 is a contact binary with strong magnetic activity. Meanwhile, we determined that KIC 9470175 and KIC 9533706 are most likely to be cluster members; KIC 9957411 and KIC 9776718 are not members of the cluster, but background stars.2. In the open cluster NGC 6819, we found that KIC 5198934 and KIC 5374883 are the deep, low mass ratio contact binaries (q < 0.25 and f > 50%); KIC 5199489 is a contact binary with a mass ratio very close to unity. We also found that only KIC 4937217 is a member of this cluster by cross-identified, the rest of them are only in the field of NGC 6819. |
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