RUI: White Dwarfs in Cataclysmic Variables

摘要-锡永 AST 99- 01955激变变星（CV）中的白色矮（WD）星星和相关的双星聚集（吸积）来自一颗非常接近太阳的星星的富氢气体。这种携带角动量的转移气体在WD周围形成了一个明亮的旋转吸积盘。这个吸积过程是高度爆炸性的，因为来自磁盘的物质首先剪切到WD表面层，将质量，能量和自旋带入WD。这一过程的物理学知之甚少，直到最近才有可能对WD进行直接的光谱观测。然而，在矮新星爆发和类新星变星的低亮度状态之间的静止间隔期间，当质量传递速率很低时，可以直接检测到WD辐射。这是因为内部的吸积盘要么不那么突出，要么不存在。 模型大气将用于比较计算机生成的光谱与观测光谱，以确定WD表面温度，表面重力，旋转速率，自旋，加热，冷却和化学丰度的吸积大气。为了解释这一不断扩大的经验CV WD属性，WD如何响应注入的质量，能量和角动量的理论框架正在构建。 这个理论框架是基于使用的计算机代码，产生随时间变化的吸积条件下的一维和二维的演化WD模型序列。的理论模型，连同衍生的经验性质的CV WD，将提供以下问题的答案：（1）什么是物理，能量收支，加热深度和开尔文时间的吸积加热向下的光子照射，压缩，剪切混合盘物质到WD？(2)有多少WD的自旋是通过吸积盘气体的角动量转移发生的？(3)当物质只在WD的赤道区域添加时，与球面吸积相比，纬度和深度的加热如何，即1D吸积研究的准确性如何？吸积带形成了吗？如果是的话，它的表面积、深度和自旋下降的时间尺度是多少？(4)通过切向盘吸积形成的吸积带是否解释了在大多数CV中观察到的弱或缺失的边界层光度（吸积气体首先与WD相互作用的地方）？(5)自CV演化开始以来，WD发生了多少吸积加热？什么是典型的CV生命周期？CV是否会在观测到的2小时和3小时之间的轨道周期间隙中演变？(6)观测到的CV WD旋转速度分布的物理解释是什么？它们的冷却速度与单个白色矮星相比如何？非磁性CV中的WD冷却方式与磁性CV不同吗？(7)从表面温度、光度、自转速度和化学丰度模式与吸积率、CV亚型和轨道周期的关系来看，CV WD的性质和演化的全球图景是什么？该项目的研究结果将为激变变星星系统中的切向（盘）吸积提供物理见解。 结果也可能提供重要的应用在更广泛的背景下（赤道）吸积流到中央紧凑的对象在其他吸积双星和磁盘吸积对象。

Abstract - Sion AST 99-01955The white dwarf (WD) star in cataclysmic variables (CVs) and related binaries accumulates (accretes) hydrogen-rich gas from a very close sun-like star. This transferred gas, which carries angular momentum, forms a bright, swirling accretion disk around the WD. This accretion process is highly explosive as matter from the disk shears first into the WD surface layers bringing mass, energy and spin into the WD. The physics of this process is very poorly understood and until recently no direct spectroscopic observations of the WD were possible. However, during the quiescent intervals between the outbursts of dwarf novae and the low brightness states of nova-like variables, when the mass transfer rate is very low, the WD radiation can be directly detected. This is because the inner accretion disk is either much less prominent or absent. Model atmospheres will be used to compare computer-generated spectra with observed spectra to determine WD surface temperatures, surface gravities, rotation rates, spinup, heating, cooling, and chemical abundances of their accreted atmospheres. In order to interpret this expanding body of empirical CV WD properties, a theoretical framework on how the WD responds to the injection of mass, energy and angular momentum is being constructed. This theory framework is based upon the use of computer codes that produce time-dependent evolutionary WD model sequences in one dimension and two dimensions under conditions of time-variable accretion. The theoretical models, together with the derived empirical properties of CV WDs, will provide answers to the following questions:(1) What are the physics, energy budget, heating depth and Kelvin time of accretion heating by downward photon irradiation, compression, and shear mixing of disk matter into the WD?(2) How much spinup of the WD occurs through angular momentum transfer by the accreting disk gas?(3) When matter is added only in the equatorial region of the WD, how does the heating with latitude and with depth compare with spherical accretion, i.e. how accurate are the 1D accretion studies? Does an accretion belt form and, if so, what is its surface area, depth, and spindown timescale?(4) Do accretion belts formed via tangential disk accretion explain the weak or missing boundary layer luminosity (where the accreting gas first interacts with the WD), that is observed in most CVs?(5) How much accretion heating of the WD has occurred since the onset of CV evolution? What are typical CV lifetimes? Do CVs evolve across the observed orbital period gap between periods of 2 and 3 hours?(6) What is the physical interpretation of the observed distribution of CV WD rotational velocities? How do their cooling rates compare with single white dwarfs? Do WDs in non-magnetic CVs cool differently than magnetic ones? (7) What is the global picture of CV WD properties and evolution from the standpoint of their surface temperatures, luminosities, rotational velocities, and chemical abundance patterns versus accretion rate, CV subtype and orbital period?The results from the research carried out in this project will provide physical insights on tangential (disk) accretion in cataclysmic variable star systems. The results may also provide important applications in the broader context of (equatorial) accretion flows onto central compact objects in other accreting binaries and disk accreting objects.