Helioseismic Study of Solar Internal Rotation

矮新星是一种喷发变星，每隔几周到几个月就会爆发一次幅度为2-6级的重复爆发。现在人们普遍认为，矮新星的爆发可能是由激变变星中吸积盘的不稳定性引起的，即由作者(Osaki，1974)于1974年首次提出的盘不稳定性模型。非磁性激变变星的爆发行为多种多样，从非爆发类新星到矮新星的各种亚类(即U宝石型、Z凸轮型和苏乌马型)。在盘不稳定性模型的基本框架内，提出了矮新星爆发的统一模型，其中吸积盘内两种不同的内在不稳定性(即热不稳定性和潮汐不稳定性)起着重要的作用。对于吸积盘中的两种内在不稳定性，在轨道周期-传质速率图上将非磁性激变变量按稳定性行为的不同组合划分为四个区域，并在图中基本了解了它们不同的爆发行为。特别是，SU-UMA型矮新星的爆发可以用热-潮汐不稳定性模型来理解，在该模型中，吸积盘中两个固有不稳定性的耦合起着独特的作用。周期间隔以下突变变星的丰富的爆发行为(即从“恒定超峰”开始，到类Z Cam的SU-ma星、“ER Uma”星，再到普通SU-ma星，最后到WZ-SGE星)，被热潮不稳定性模型所理解。

Dwarf novae are eruptive variables showing repetitive outbursts of amplitudes of 2-6 magnitude once every a few weeks to months. It is now widelyu accepted that outbursts of dwarf novae may be caused by the instability in accretion disks in cataclysmic variable stars : i.e., the disk instability model which was first proposed by the present author (Osaki, 1974) in 1974. There is a rich variety in outburst behaviors of non-magnetic cataclysmic variable stars, starting from non-outbursting nova-like stars to various sub-classes of dwarf novae (i.e., U Gem-type, Z Cam-type, and SU UMa-type). Furthermore, two extreme cases of SU UMa-type dw arf novaehave recently been recognized : WZ Sge-type and ER UMa-type.A unification model for dwarf nova outbursts is proposed within the basic framework of the disk instability model in which two different intrinsic instabilities (i.e., the thermal instability and the tidal instability) within accretion disks play an essential role. Non-magnetic cataclysmic variables are classified into four regions in orbital-period versus mass-transfer rate diagram in different combination of stability behavior for the two intrinsic instabilities in accretion disks, and their different outburst behaviors are basically understood in this diagram. In particular, outbursts in SU UMa-type dwarf novae are understood by the thermal-tidal instability model in which the coupling of the two intrinsic instabailities in accretion disks plays a unique role. A rich variety of outburst behavior of cataclysmic variables below the period gap (i.e., starting from "parmanent superhumpers", to Z Cam-like SU UMa stars, "ER UMa stars", to ordinary SU UMa stars, finally to WZ Sge stars) is understood by the thermal-tidal instability model.