Detailed studies of hot subdwarf B (sdB) stars with red dwarf (dM) or brown dwarf (BD) companions can shed light on the effects of binarity on late stellar evolution. Such systems exhibit a strong, quasi-sinusoidal reflection effect due to irradiation of the cool companion, and some even show primary and secondary eclipses. For this work, we computed Fourier transforms of TESS light curves of sdB+dM/BD binaries and investigate correlations between the relative amplitudes and phases of their harmonics and system parameters. We show that the reflection effect shape strongly depends on the orbital inclination, with nearly face-on systems having much more sinusoidal shapes than nearly edge-on systems. This information is encoded by the relative strength of the first harmonic in the Fourier transform. By comparing observations of solved systems to synthetic light curves generated by lcurve, we find that the inclination of non-eclipsing systems with high signal-to-noise light curves can be determined to within ≈10° simply by measuring their orbital periods and first harmonic strengths. We also discovered a slight asymmetry in the reflection effect shape of sdB+dM/BD binaries using the relative phase of the first harmonic. From our analysis of synthetic light curves, we conclude the asymmetry results from relativistic beaming of both stellar components. This marks the first time Doppler beaming has been detected in sdB+dM/BD systems. Although advanced modeling is necessary to quantify the effects of secondary parameters, such as limb darkening, the temperature ratio, and the radius ratio on the reflection effect shape, our pilot study demonstrates that it might be possible to extract both the inclination angle and cool companion velocity from the light curves of non-eclipsing systems.

中文翻译：

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从太空观测到的紧密双星中的热亚矮星


对具有红矮星 (dM) 或棕矮星 (BD) 伴星的热亚矮星 B (sdB) 恒星的详细研究可以揭示双星对晚期恒星演化的影响。由于冷伴星的照射，此类系统表现出强烈的准正弦反射效应，有些甚至表现出初食和次食。在这项工作中，我们计算了 sdB+dM/BD 双星的 TESS 光变曲线的傅里叶变换，并研究了其谐波的相对幅度和相位与系统参数之间的相关性。我们表明，反射效应形状很大程度上取决于轨道倾角，近正面系统比近边缘系统具有更多的正弦形状。该信息通过傅里叶变换中一次谐波的相对强度进行编码。通过将已求解系统的观测结果与 lcurve 生成​​的合成光变曲线进行比较，我们发现，只需测量其轨道周期和一次谐波，即可将具有高信噪比光变曲线的非食系统的倾角确定在 ≈10° 以内的优势。我们还使用一次谐波的相对相位发现 sdB+dM/BD 双星的反射效应形状存在轻微的不对称性。根据我们对合成光变曲线的分析，我们得出了两个恒星成分的相对论光束的不对称性结果。这标志着首次在 sdB+dM/BD 系统中检测到多普勒波束。 尽管需要先进的建模来量化次要参数的影响，例如临边变暗、温度比和半径比对反射效果形状的影响，但我们的试点研究表明，有可能提取倾斜角和冷伴星来自非食系统光变曲线的速度。