密近双星系统中三颗活动红巨星：V2253 Oph，IT Com和IS Vir的长期测光
Long-term photometry of three active red giants in close binary systems: V2253 Oph, IT Com and IS Vir
摘要：
我们提出并分析了三个活跃的恒星V2253 Oph，IT Com和IS Vir的长期光学光度测量。这三个系统都是单线光谱双星，早期的K巨星是主要成分，但处于不同的轨道旋转同步阶段。我们的光度测量由2 MASS和WISE近红外和中红外星等补充，然后用于获得更准确的有效温度和折射率。对于V2253 Oph和IT Com，我们发现它们的光谱能量分布与纯光球辐射一致。对于IS Vir，我们检测到一个边缘的中红外过量，这暗示了尘埃盘。IT Com的轨道和旋转平面似乎是共面的，与文献中以前的研究结果相反。我们应用多频分析技术来确定光度周期，并可能改变的时期，从几天到几十年。新的自转周期分别为21.55 ± 0.03d、65.1 ± 0.3d和23.50 ± 0.04d。这些周期的分裂导致V2253 Oph的Δ P/P ~0.02和IT Com的Δ P/P ~ 0.07的差异表面旋转的初步检测。利用基于短时傅立叶变换的时频分析技术，我们给出了V2253 Oph周期光变化的证据，其周期光变化的长度为10年，IS Vir为5- 6年。一个单一的触发器事件已观察到的IT Com的持续时间2- 3年。它的主活动经度的交换发生在接近近星点通过的时刻，表明轨道动力学对磁活动的某种响应。V2253 Oph的21.55-d旋转调制也显示了与轨道周期的相位相干性，轨道周期是旋转周期的15倍，因此也表明了与恒星磁活动的潮汐反馈。
英文摘要：
We present and analyze long-term optical photometric measurements of the three active stars V2253 Oph, IT Com and IS Vir. All three systems are single-lined spectroscopic binaries with an early K giant as primary component but in different stages of orbital-rotational synchronization. Our photometry is supplemented by 2MASS and WISE near-IR and mid-IR magnitudes and then used to obtain more accurate effective temperatures and extinctions. For V2253 Oph and IT Com, we found their spectral energy distributions consistent with pure photospheric emission. For IS Vir, we detect a marginal mid-IR excess which hints towards a dust disk. The orbital and rotational planes of IT Com appear to be coplanar, contrary to previous findings in the literature. We apply a multiple frequency analysis technique to determine photometric periods, and possibly changes of periods, ranging from days to decades. New rotational periods of 21.55+-0.03d, 65.1+-0.3d, and 23.50+-0.04d were determined for V2253 Oph, IT Com, and IS Vir, respectively. Splitting of these periods led to tentative detections of differential surface rotations of delta P/P ~0.02 for V2253 Oph and 0.07 for IT Com. Using a time-frequency technique based on short-term Fourier transforms we present evidence of cyclic light variations of length ~10yrs for V2253 Oph and 5-6yrs for IS Vir. A single flip-flop event has been observed for IT Com of duration 2-3yrs. Its exchange of the dominant active longitude had happened close to a time of periastron passage, suggesting some response of the magnetic activity from the orbital dynamics. The 21.55-d rotational modulation of V2253 Oph showed phase coherence also with the orbital period, which is 15 times longer than the rotational period, thus also indicating a tidal feedback with the stellar magnetic activity.
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