BO Ceti: Dwarf nova showing both IW And-type and SU UMa-Type features
BO Ceti: Dwarf nova showing both IW And-type and SU UMa-Type features
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DOI：
10.1093/pasj/psab074
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发表时间：
2021-06
影响因子：
2.3
通讯作者：
Taichi Kato;Y. Tampo;N. Kojiguchi;M. Shibata;Junpei Ito;K. Isogai;H. Itoh;F. Hambsch;B. Monard-B.
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作者：
Taichi Kato;Y. Tampo;N. Kojiguchi;M. Shibata;Junpei Ito;K. Isogai;H. Itoh;F. Hambsch;B. Monard-B.
IW和恒星是最近被确认的矮新星的一个亚群，其特征是（经常重复）缓慢上升的静止，以增亮结束，但这种变化的确切机制尚未确定。根据2019-2020年期间的行为，我们已经将被认为是新星激变变星的BO Cet确定为IW And星的新成员。除此之外，该天体在2020-2021年还显示出矮新星型爆发，并且在至少一次长爆发期间形成了周期比轨道周期长7.8%的超级驼峰。该天体已被证实是一颗SU UMa型矮新星，具有异常长的轨道周期（0.1398 d）。因此，BO Cet是第一个同时显示SU UMa型和IW And型特征的激变变星。我们从生长阶段的超峰（A阶段超峰）中获得了0.31-0.34的质量比（q）。在这个q值下，导致潮汐不稳定和超级驼峰的3：1共振半径与潮汐截断半径非常相似。我们解释说，在某些情况下，这个对象显示IW和型变化时，磁盘的大小是不够大，但3：1的共振半径可以达到作为一个结果的热不稳定性。我们还讨论了有SU UMa型矮新星以上q = 0.30，这是高于以前考虑的限制（10.25）来自数值模拟，这是可能的，因为3：1共振的半径是潮汐截断半径内。我们约束的白色矮星的质量大于1.0兆焦耳，这可能是负责IW和型行为和观测到的强度的He ii发射。然而，这个天体之所以独特的确切原因是它同时显示了SU UMa型和IW And型的特征，这一点仍然没有得到解决。
IW And stars are a recently recognized subgroup of dwarf novae which are characterized by (often repetitive) slowly rising standstills terminated by brightening, but the exact mechanism for this variation is not yet identified. We have identified BO Cet, which had been considered as a novalike cataclysmic variable, as a new member of IW And stars based on its behavior in 2019–2020. In addition to this, the object showed dwarf nova-type outbursts in 2020–2021, and superhumps that had periods $7.8\%$ longer than the orbital one developed during at least one long outburst. This object has been confirmed as an SU UMa-type dwarf nova with an exceptionally long orbital period (0.1398 d). BO Cet is thus the first cataclysmic variable showing both SU UMa-type and IW And-type features. We obtained a mass ratio (q) of 0.31–0.34 from the superhumps in the growing phase (stage A superhumps). At this q, the radius of the 3 : 1 resonance, responsible for tidal instability and superhumps, and the tidal truncation radius are very similar. We interpret that in some occasions this object showed IW And-type variation when the disk size was not large enough, but that the radius of the 3 : 1 resonance could be reached as a result of thermal instability. We also discuss that there are SU UMa-type dwarf novae above q = 0.30, which is above the previously considered limit (∼0.25) derived from numerical simulations and that this is possible since the radius of the 3 : 1 resonance is inside the tidal truncation radius. We constrained the mass of the white dwarf larger than 1.0 M⊙, which may be responsible for the IW And-type behavior and the observed strength of the He ii emission. The exact reason, however, why this object is unique in that it shows both SU UMa-type and IW And-type features is still unsolved.