双星与变星研究组知识库

Near-contact binaries (NCB) are interesting with their marginal contact nature, i.e., one or both of the components at or close to the critical Roche Lobe. Once a component fills its critical Roche Lobe, mass transfer will occur. Therefore, NCBs are good targets to study mass transfer occurring in close binaries. We thus investigated a group of NCBs and found that the light curves of NCBs with primary components filling their critical Roche Lobe always show enhanced luminosity around the left shoulder of secondary minimum in their light curves and decreasing orbital periods. This implies that the mass transfer plays an important role in the evolution of NCBs. On the other hand, only a few systems are found to have asymmetric light curves among NCBs with secondary components filling their critical Roche Lobe. And the detected amplitude of reducing magnitude of them are very small, not more than 0.01 mag in V band. However, the amplitude of reducing magnitude found in other type NCBs are all larger than 0.01 mag. This may suggest that the mass transfer from the primary component to the secondary one is stronger than that from the opposite direction. Furthermore, we investigated some related systems, i.e. W UMa overcontact binaries and high fill-out extreme mass Ratio overcontact binary systems, and suggested an evolutionary sequence with case A mass transfer.