Instabilities of Accretion Disks in Cataclysmic Variable Stars

灾变变星中吸积盘的不稳定性

• 批准号: 01460008
• 负责人: OSAKI Yoji
• 金额: $ 3.33万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1989
• 资助国家: 日本
• 起止时间: 1989 至 1991
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-01460008/
• 关键词: accretion disks; cataclysmic variable stars; dwarf novae; instabilities; hydrodynamic simulations; eigenvalue problems; tidal effects; SU UMa stars; SU UMa型星; U Gem型星; SU UMの型星; レゾナンス

Dwarf novae are eruptive variable stars showing repetitive outbursts of amplitudes of 2-6 magnitude, outburst duration of a few days to 20 days, and recurrence time of 20-300 days. They belong to a more general class of cataclysmic variable stars, in that a Roche lobe filling cool dwarf star loses mass through the inner Lagrangian point and a non-magnetic white dwarf star accretes it through an accretion disk. Various outbursting phenomena occurring in these stars are now thought to be caused by variable accretion onto the white dwarf In this research, we have investigated the outburst mechanisms of dwarf novae based on intrinsic instabilities within the accretion disks in cataclysmic variable stars.Two kinds of instabilities are known in acceretion disks of dwarf novae ; the thermal instability (i. e., the ordinary disk instability) and the tidal instability. The thermal instability is an instability which occurs in the outer-parts of accretion disk of dwarf nova when the temperature … More of the disk becomes cool enough for hydrogen to recombine. This thermal instability leads to a thermal relaxation oscillation of the accretion disk by periodically accumulating matter in the disk and then suddenly dumping it onto the white dwarf, giving rise to sudden burst of accretion luminosity. This mechanism is now believed to be responsible for the ordinary outburst of U Gem-type dwarf novae. - Another kind of instability in accretion disks is the tidal instability by which instability an accretion disk is deformed into a precessing eccentric disk due to the tidal effects of the secondary star. In what follows, we list problems that we have examined in this research project and results obtained.(1) We have proposed a new model that explains the superoutburst phenomenon in SU UMa-type dwarf novae. This model is based on the combined mechanisms of the thermal instability and the tidal instability of accretion disk.(2) We have studied time evolution of accretion disk radius in the outburst cycle of dwarf nova. We examined this based on both the mass transfer burst model and the disk instability model. It was found that the disk instability model is more favorable in explaining observed disk radius variation than the mass transfer burst model.(3) Two-dimensional hydrodynamic simulations have been performed to study the tidal instability of accretion disks in cataclysmic variable stars. Two different methods of hydrodynamic simulations are used ; one is the viscous particle method and the other is the smoothed particle hydrodynamics abbreviated as SPH method). It has been found that an accretion disk is deformed to a precessing eccentric form if the mass of the secondary star is less than about one-fourth of the mass of the primary star.(4) The precession rate of the eccentric disk is studied. It is shown that the precession rate can be formulated as an eigenvalue problem of one-armed oscillation of the accretion disk. Less

矮新星是爆发变星，重复爆发的幅度为2 - 6等，爆发持续时间为几天到20天，重复时间为20 - 300天。它们属于更一般的激变变星，因为充满洛希瓣的冷矮星星星通过内拉格朗日点失去质量，而非磁性白矮星星星通过吸积盘吸积它。在激变变星的吸积盘中存在着两种不稳定性，即热不稳定性（即吸积盘内的不稳定性）和热不稳定性（即吸积盘内的不稳定性）。例如，普通盘不稳定性）和潮汐不稳定性。热不稳定性是当温度升高时发生在矮新星吸积盘外部的不稳定性 ...更多信息 温度降低到足以让氢重新结合这种热不稳定性导致吸积盘的热弛豫振荡，周期性地在盘中积累物质，然后突然将其倾倒到白色矮星上，引起吸积光度的突然爆发。这种机制现在被认为是造成U Gem型矮新星爆发的原因。- 吸积盘中的另一种不稳定性是潮汐不稳定性，通过这种不稳定性，吸积盘由于次级星星的潮汐效应而变形为进动偏心盘。在下文中，我们列出了我们在本研究项目中研究的问题和获得的结果。(1)我们提出了一个新的模型来解释超爆发现象的SU UMa型矮新星。该模型是基于吸积盘的热不稳定性和潮汐不稳定性的联合机制。(2)研究了矮新星爆发周期中吸积盘半径的时间演化。我们研究了这两个传质爆发模型和磁盘不稳定性模型的基础上。结果表明，圆盘不稳定性模型比传质猝发模型更能解释圆盘半径的变化。(3)利用二维流体动力学模拟研究激变变星吸积盘的潮汐不稳定性。采用了两种不同的流体动力学模拟方法，一种是粘性粒子法，另一种是光滑粒子流体动力学（简称SPH法）。已经发现，如果次级星星的质量小于初级星星质量的四分之一，则吸积盘变形为进动偏心形式。(4)研究了偏心圆盘的进动率。结果表明，旋进率可以用吸积盘单臂振动的本征值问题来表示。少

项目成果

Y.Osaki: "Excitation Mechanisms of Solar Oscillations." Progress of Seismology of the Sun and Stars,ed.Y.Osaki and H.Shibahashi(Springer-Verlag). 75-86 (1990)

Y.Osaki：“太阳振荡的激发机制。”

P.Szkody: "Ginga Observations of the Dwarf Novae BV Pup and V426 Oph." Asrtron.J.100. 546-553 (1990)

P.Szkody：“矮新星 BV Pup 和 V426 Oph 的银河观测。”

H.Shibahashi: "Introductory Review of Oscillations of the Sun and Srars" Progress of seismology of the Sun and Stars eds.Y.Osaki & H.Shibahashi(Springer-Verlag). 2-22 (1990)

H.Shibahashi：“太阳和星体振荡的介绍性回顾”太阳和恒星地震学的进展编辑Y.Osaki

H. Shibahashi: "Theoretical Aspects of Asteroseismology of the Rapidly Oscillating Ap Strars." Challenges to Theories of the Structure of Moderate Mass Stars. Springer-Verlag. 393-410 (1991)

H. Shibahashi：“快速振荡的 Ap Strars 星震学的理论方面。”

Y. Osaki: "A Model for the Superoutburst Phenomenon of SU UMa Stars." Publ.Astron.Soc.Japan. 41. 1005-1033 (1989)

Y. Osaki：“SU UMa 星超级爆发现象的模型。”