First multi-colour complete light curves and low-resolution spectra of short-period eclipsing binary TT Cet are presented. The stellar atmospheric parameters of the primary star were derived through spectra fitting as: $T_{eff}=7\,091\pm124\,{\text{K}}$ , $\log g = 4.15\pm0.33\,{\text{cm}}/\text{s}^2$ , and $[Fe/H]=-0.23\pm0.04\,\text{dex}$ . The light curves were analysed using the Wilson–Devinney code. The photometric solution suggests that this target should be a near-contact binary with the primary component filling its critical Roche lobe (i.e. SD1-type NCB). The luminosity enhancement around the primary light maximum (phase 0.10–0.40) on the light curve was detected like other SD1-type NCBs, which could be caused by a hot spot near the facing surface of the secondary component due to mass transfer. Long-term decrease of the orbital period at a rate of $dP/dt=-5.01\,({\pm}0.06)\times 10^{-8}\,{{\text{d}} \cdot{yr}}^{-1}$ was detected by the O–C analysis, which supports the mass transfer from the primary to the secondary and is consistent with its primary filling configuration. No third body was found through the light curve and O–C analysis. TT Cet may locate in the broken contact stage predicted by the thermal relaxation oscillation theory (TRO) and will evolve to the contact stage eventually. It is another good observational example supporting the TRO theory. We have collected all known SD1-type NCBs with absolute parameters from the literatures. The relations of these parameters are summarised for these rare systems.

中文翻译：

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传质近接触二元TT Cet的研究

首次提出了短周期食二元TT Cet的多色完整光变曲线和低分辨率光谱。主星的恒星大气参数通过光谱拟合得到： $T_{eff}=7\,091\pm124\,{\text{K}}$ , $\log g = 4.15\pm0.33\,{\text{cm}}/\text{s}^2$ ， 和 $[Fe/H]=-0.23\pm0.04\,\text{dex}$ . 使用 Wilson-Devinney 代码分析光变曲线。光度解决方案表明，该目标应该是一个近接触双星，主要成分填充其关键的罗氏瓣（即 SD1 型 NCB）。与其他 SD1 型 NCB 一样，检测到光度曲线上初级光最大值（相位 0.10-0.40）附近的光度增强，这可能是由于传质引起的次级组件面对表面附近的热点引起的。轨道周期的长期减少速度为 $dP/dt=-5.01\,({\pm}0.06)\times 10^{-8}\,{{\text{d}} \cdot{yr}}^{-1}$ 通过 O-C 分析检测到，这支持从初级到次级的质量传递，并且与其初级填充配置一致。通过光变曲线和 O-C 分析没有发现第三具尸体。TT Cet可能处于热弛豫振荡理论（TRO）预测的接触断裂阶段，最终会演化到接触阶段。这是支持 TRO 理论的另一个很好的观察例子。我们从文献中收集了所有已知的具有绝对参数的 SD1 型 NCB。为这些稀有系统总结了这些参数的关系。