This is a study of spectral and photometric observations of the binary system with an X-ray component V725 Tauri=A0535+262. It consists of a giant star HDE 245770 of spectral class O9.7 and the pulsar A0535+26 with a pulsation period of ~103 s. Active stages of this object, accompanied by “giant” X-ray outbursts, have been observed repeatedly. The last events occurred during 2009-2011. Our studies in 2017-2020 yielded the following data: over the last three years the B and V band brightness of the object has remained at a high level and began to decrease at the end of 2019. Here, beginning in 2016 a gradual increase in the radiative fluxes in the Hβ and Hα emission lines has been observed. At present the equivalent widths of these lines exceed the values recorded during the time of the gigan X-ray outburst of 2011. Previous studies have shown that a similar combination of the characteristics of this object, specifically an increase in emission line fluxes as the brightness decreases. is detected just before the onset of an active stage.

中文翻译：

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Be/X 射线二元物体的光度和光谱研究 V725 Tau=A0535+262

这是对具有 X 射线分量 V725 Tauri=A0535+262 的双星系统的光谱和光度观测的研究。它由光谱等级为 O9.7 的巨星 HDE 245770 和脉动周期约为 103 秒的脉冲星 A0535+26 组成。这个物体的活跃阶段，伴随着“巨大的”X射线爆发，已经被反复观察到。最近的事件发生在 2009-2011 年。我们在 2017-2020 年的研究得出了以下数据：过去三年，天体的 B 和 V 波段亮度一直保持在较高水平，并在 2019 年底开始下降。这里，从 2016 年开始逐渐增加已观察到 Hβ 和 Hα 发射线中的辐射通量。目前，这些线的等效宽度超过了 2011 年巨型 X 射线爆发期间记录的值。先前的研究表明，该物体的特征组合类似，特别是随着亮度的降低，发射线通量会增加。在活动阶段开始之前检测到。