| 其他摘要 | Near Contact Binaries (NCBs) are a sub-type of close binary systems in which both components have filled or nearly fill their Roche lobes. In the systems, both components have high filling-degree to their Roche lobes, while a common convective envelope has not yet formed, along with the surface temperature difference between the two stars is large. The study on NCBs is helpful for researchers to explore the process of the formation of contact binaries. In particular, NCBs with the primary component filling its Roche lobes (SD1s) show obvious characteristics of mass transfer. The mass transfer from the primary component to the secondary, results in a long-term decrease of the orbital period of these systems, accompanied by the light curve distortion in the corresponding phase. Therefore, the SD1s are served as ideal laboratories for studying mass exchange between the two components of binaries. However, because such NCBs are in the stage of rapid mass transfer and have a very short evolutionary time scale, there are few such samples available at present. In addition, NCBs of the poor-thermal contact are the ones where both components have filled their Roche Lobes, while large temperature difference exists (hereinafter poor-thermal contact binaries). Both the SD1s and the poor-thermal contact binaries, are believed to be the two stages that predicted by the theory of Thermal Relaxation Oscillation (TRO), and are significant to test the theory of TRO. However, samples of these two types of NCBs are very limited, and the short-period samples are scarce among them, which causes a challenge to the theory of TRO. In this paper, in order to find out more such two kinds of NCBs, we conducted observation studies on a batch of objects, and carries out the preliminary statistical analysis based on the currently available samples, obtaining the main results that are as follows: Using the W-D code to analyse the light curves of V505 Cyg, combined with the period analysis, it is found that it is an SD1 system. The primary maximum of its light curve is higher than the secondary, which signifies that the mass flow is transferred from the more massive star to the less massive one, causing locally high-temperature regions on the surface of the latter one. In addition, its secular decreasing orbital period can also be explained as that the matter is transferring from the more massive star to its companion. Apart from the secular decrease of the orbital period, a periodic oscillation also exists. With the period analysis, the Light Travel Time Effect (LTTE) of a third body is believed to be the most probable cause to lead to the periodic oscillation of V505 Cyg. As the orbital period shrinkage, V505 Cyg will evolve into a contact binary. V505 Cyg now may also lie in a stage predicted by the TRO theory, and is currently evolving towards a contact binary system. By conducting two observations on J115114, we obtained two complete sets of light curves in the BVRI bands with the interval of about two years, and fitted those two sets of light curves with the W-D code. Both results showed that J115114 is an SD1 as well. Especially, its mass ratio is less than 0.2. Such a low mass ratio indicates that J115114 is likely to have experienced at least one TRO cycle, and it may have went through the mass ratio reversal. Currently, it is probable in the phase of contact-broken predicted by the TRO theory, or at the beginning of mass transfer from the primary component to the secondary. In addition, with all available eclipsing timings, the analysis of O - C manifests that its orbital period is decreasing continuously, which agrees with the configuration derived with the W-D code. As the orbital period decreases, J115114 will finally evolve into a contact binary. We fitted the multi-filter light curves observed with the Sino-Thai 70cm telescope with the W-D code, finding that V0749 Aur is a poor-thermal contact binary, where both the two components have high filling degree of their Roche lobes, while significant temperature difference between them exists. Based on the sky survey data, we have revised its period. In addition, the analysis with W-D code showed a large contribution of a third light. By querying the Gaia astrometric parameters, we confirmed that the third light in the photometric solution is from a background star. The Gaia astrometric parameters show that the background star and V0749 Aur have similar coordinate，while they have quite different parallaxes. Therefore, they cannot be gravitationally bound, but are in the same direction of the sight line. We applied the W-D code to fit the high-precision photometric data of V719 Her from TESS and other from the ground-based sky survey telescopes, finding that V719 Her is also a poor-thermal contact binary with a small degree of contact. The light curves of V719 Her belong to the EB type, which indicates that it has not yet reached the thermal-contact state. Its light curves change rapidly over time, and the W-D fitting shows that a cool spot which rapidly changes its positions and radii on the primary component, leads to the continuous changes of the light curves of V719 Her. V719 Her is a late-type (G3-type spectra) binary with strong magnetic activities, and the Hα emission line from its spectrum also confirmed its magnetic activities. In addition, its orbital period is decreasing, which, based on our calculations, is believed to be the result of the cooperation of the angular momentum loss and mass transfer between the system. In addition, the O-C analysis shows that there is a periodic oscillation in its orbital period, which may be caused by the LTTE of a third body or by magnetic activities. Applying the sky-survey data, we have updated the orbital period-variation analyses of two W UMa contact binaries: HH UMa and V1175 Her. For the first time, the periodic oscillations of their O-C data were detected. Our analysis suggests that the LTTE of a third body is the most probable cause of the periodic oscillations of these two systems. In particular, the minimum mass of the third body in V1175 Her is greater than the mass of the less massive component of V1175 Her, indicating that the less massive one of the binary system was not replaced by the third body, thus V1175 He retains the original dynamic information. We have collected all reported samples of the SD1, along with some poor-thermal contact binaries in this work. The statistical analysis manifests that there is a linear relationship between the period and the rate of the period change of the SD1s. Combined with the samples of contact binaries collected by other researchers, the distributions of the period, total mass, total orbital angular momentum and mass ratio of these three binaries are compared. Based on the available samples, the conclusion from the statistical analysis reveals that the peak value of the period of contact binaries is smaller than those of the two types NCBs, and its period distribution is almost symmetrical. However, the periods of SD1s and poor-thermal contact binaries are generally distributed in the long period (P>0.45 d) region, and there are two peaks. In addition, the overall distributions of the total mass and total orbital angular momentum of the SD1s are larger than those of the poor-thermal contact binaries and contact binaries. However, the distribution of orbital period, total mass, and total angular momentum of SD1s and poor-thermal contact binaries overlap among most regions. As for the mass ratio, the peak value of the SD1s is larger than those of the poor-thermal contact binaries and contact binaries, while the difference between the latter two is very small. |
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