The Cause of the Superoutburst in SU UMa Stars is Finally Revealed by Kepler Light Curve of V1504 Cygni
The Cause of the Superoutburst in SU UMa Stars is Finally Revealed by Kepler Light Curve of V1504 Cygni
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天鹅座V1504开普勒光曲线终于揭示SU UMa星超级爆发的原因
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发表时间：
2012
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通讯作者：
Taichi Kato
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作者：
Y. Osaki;Taichi Kato
本文研究了天鹅座SU Uma星星V1504的SC（shortcadence）Kepler光变曲线，其周期约为630 d。天鹅座V1504的所有超爆发都被证明是主爆发类型，并且超峰首先出现在前兆的最大值附近。超峰从前兆到主超爆的平滑增长表明，超爆是由大崎（1989）提出的热潮汐不稳定性（TTI）模型所设想的潮汐不稳定性（如增长的超峰所证明的）引发的。我们对V1504 Cyg的光变曲线进行了功率谱分析。其中一个突出的特征是出现了一个负的超峰，其长度约为300 d，远远超过了一个超循环。我们发现，负超峰的出现往往会降低正常爆发的发生频率。在天鹅座V1504中发现了两种类型的超循环，它们与Smak（1985）提出的SU Uma星星VW Hyi的光变曲线中的L型和S型超循环相似。结果表明，L型超循环是伴随负超峰的超循环，S型超循环是不伴随负超峰的超循环。如果我们采用一个倾斜的盘作为负超峰的起源，两种类型的超循环被理解为是由于爆发间隔的不同，这反过来又是由次级盘到盘的不同部分的质量供应的差异引起的。在天鹅座V1504的一个超循环中，负超峰的频率系统地变化。这种变化可以被用作盘半径变化的指标，我们已经发现，在V1504天鹅座观测到的盘半径变化非常符合TTI模型的预测。
We have studied the SC (short cadence) Kepler light curve of an SU UMa star, V1504 Cyg, which extends for a period of about 630 d. All superoutbursts in V1504 Cyg have turned out to be of the precursor-main type and the superhump first appears near the maximum of the precursor. The superhumps grow smoothly from the precursor to the main superoutburst showing that the superoutburst is initiated by the tidal instability (as evidenced by growing superhump) as envisioned in the thermal-tidal instability (TTI) model proposed by Osaki (1989). We have performed power spectral analysis of the light curve of V1504 Cyg. One of outstanding features is an appearance of a negative superhump extending for around 300 d, well over a supercycle. We have found that an appearance of the negative superhump tends to reduce the frequency of occurrence of normal outbursts. Two types of supercycles are recognized in V1504 Cyg, which are similar to those of the Type L and S supercycles in the light curve of VW Hyi, a prototype SU UMa star, introduced by Smak (1985). It is found that the Type L supercycle is the one accompanied with the negative superhump and the Type S is that without the negative superhump. If we adopt a tilted disk as an origin of the negative superhump, two types of the supercycles are understood to be due to a difference in outburst intervals, which is in turn caused by a difference in mass supply from the secondary to different parts of the disk. The frequency of the negative superhump varies systematically during a supercycle in V1504 Cyg. This variation can be used as an indicator of the disk radius variation and we have found that observed disk radius variation in V1504 Cyg fits very well with a prediction of the TTI model.