Unified Model of Outbursts in Dwarf Novae

矮新星是爆发性变星，其重复爆发的幅度为2-6级。在矮新星中有三个子类：U Gem型仅显示普通爆发，Z Cam型显示偶尔静止，SU UMa型显示超级爆发。本研究的主要目的是检验我们是否可以用一个统一的范式：所谓的盘不稳定性模型来解释矮新星中丰富多样的爆发现象。为此，我们利用吸积盘的热不稳定性和潮汐不稳定性的联合机制对SUUMa星的超爆发现象进行了详细的数值模拟。研究发现，该模型可以成功地再现SU UMa星的超爆发周期。我们已经制定了吸积盘的潮汐偏心不稳定性的单臂模式的吸积盘的振荡的本征值问题，我们已经研究了本征值和本征函数的这种模式的数值和解析。本文研究了SU UMa型矮新星的盘不稳定性模型与WZ Sge型矮新星的关系，这种矮新星只表现出超爆发，但显然没有正常爆发。最极端的星星的WZ Sge本身的一个特殊情况下进行了讨论，并建议作为一个极端的情况下，非常低的粘度在静止和相当低的质量传递速率从第二。

Dwarf novae are eruptive variables showing repetitive outbursts of amplitudes of 2-6 magnitude. There are three sub-classes in dwarf novae : the U Gem-type showing only the ordinary outbursts, the Z Cam-type showing occasional standstill, and the SU UMa-type showing superoutbursts. The main purpose of this research is to examine whether or not we can explain rich variety of outburst phenomena in dwarf novae by a unified paradigm : the so-called disk instability model. To this end, we have made detailed numerical simulations of the superoutburst phenomenon of SU UMa stars by the combined mechanism of the thermal and tidal instabilities of accretion disks. It has been found that the superoutburst cycle of SU UMa stars can be successfully reproduced by this model. We have formulated the tidal eccentric instability of an accretion disk as an eigenvalue problem of the oscillation of the one-armed mode in the accretion disk and we have examined the eigenvalue and eigenfunction of this mode both numerically and analytically. The disk instability model for SU UMa-type dwarf novae is examined in relation to the WZ Sge-type dwarf novae which exhibit only superoutbursts but apparently no normal outburst. A particular case of the most extreme star of WZ Sge itself is discussed and it is suggested as an extreme case of very low viscosity in quiescence and of rather low mass transfer rate from the secondary.