White Dwarfs in Cataclysmic Variables: Probes of Evolution and Accretion Physics

灾难变星中的白矮星：演化和吸积物理学的探索

• 批准号: 0807892
• 负责人: Edward Sion
• 金额: $ 21.49万
• 依托单位: Villanova University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0807892&HistoricalAwards=false
• 关键词: White; Dwarfs; Cataclysmic; Variables; Probes

A cataclysmic variable is a compact binary (with a period less than twelve hours) in which the primary (a white dwarf) accretes matter and angular momentum from the secondary star (a main sequence star) filling its Roche-lobe. In non-magnetic systems, the matter is transferred, at continuous or sporadic rates, by means of an accretion disk around the white dwarf. Ongoing accretion at a low rate (quiescence) is interrupted every few weeks to months by intense accretion (outburst) of days to weeks, and every few thousand years by a thermonuclear explosion (a classical nova event). Thus the white dwarfs in these systems are probes of cataclysmic evolution and accretion physics because they bear the thermal, chemical and rotational imprint of their long-term accretion and explosive thermonuclear history. Here, Professor Sion, accompanied by collaborators and students, will examine white dwarfs in cataclysmic binaries and make measurements of their surface temperatures, rotation rates and chemistry of their accreted atmospheres, using multi-component synthetic spectral fitting. This will allow them to probe the age, evolutionary history, time-averaged accretion rate, white dwarf mass and core temperature, and the mass transfer driving mechanisms in these systems. In particular, measurements of photospheric chemical abundances will test accretion and diffusion theories, while overabundances of thermonuclear-processed elements could indicate pre-historical nova explosions or processed core material from an originally more massive secondary. The distribution of white dwarf rotation rates above and below the period gap, which will be explored here, is key to understanding the physics of angular momentum transfer during accretion. Through this project they will also enlarge the sample of white dwarfs with known surface temperatures across all cataclysmic variable subtypes. They will carry out evolutionary accretion simulations with time-variable accretion and thus provide a new and independent means of determining white dwarf masses, constraining white dwarf rotation velocities, and determining the thermal impact that prolonged accretion heating has on the white dwarfs. An understanding of the consequences of accretion in cataclysmic variables is the first step in a global understanding of accretion-related phenomena throughout the universe (e.g. around neutron stars and black holes) which cannot be easily observed. Also the ejected material into the interstellar medium from novae explosions, and hence the composition of the outer envelopes of white dwarfs in cataclysmic variables, tells us about which elements (metals) are expected to be recycled in the interstellar medium for the next generation of stars. In addition, some cataclysmic variable systems are possible progenitors for Type Ia supernovae and changes in our understanding of these accreting white dwarfs translates into change in the possible size of the population from which Type Ia supernovae arise. Throughout this project, undergraduate students will play key roles in the analysis and synthetic spectral modeling of the data. They will also participate in the dissemination of the results via presentation of poster papers at professional meetings and co-authoring refereed publications.

激变变星是一颗紧凑的双星（周期小于12小时），其中主星（白色矮星）吸积了次级星星（主序星星星）的物质和角动量，填充了它的罗奇瓣。在非磁性系统中，物质通过围绕白色矮星的吸积盘以连续或零星的速率转移。正在进行的低速吸积（静止）每隔几周到几个月就会被几天到几周的强烈吸积（爆发）打断，每隔几千年就会被热核爆炸（经典的新星事件）打断。因此，这些系统中的白色矮星是激变演化和吸积物理学的探针，因为它们带有长期吸积和爆炸热核历史的热、化学和旋转印记。在这里，锡永教授将在合作者和学生的陪同下，研究灾难性双星中的白色矮星，并使用多组分合成光谱拟合测量其表面温度，旋转速率和吸积大气的化学性质。这将使他们能够探测这些系统的年龄，演化历史，时间平均吸积速率，白色矮星质量和核心温度，以及质量转移驱动机制。特别是，测量光球化学丰度将检验吸积和扩散理论，而热核处理元素的过度丰度可能表明史前新星爆炸或来自原始更大质量的次级物质的处理核心材料。白色矮星自转速率在周期间隙上下的分布，是理解吸积过程中角动量转移物理的关键。通过这个项目，他们还将扩大已知表面温度的白色矮星的样本，包括所有灾难性的变量亚型。他们将利用时变吸积进行演化吸积模拟，从而提供一种新的独立手段来确定白色矮星的质量，限制白色矮星的旋转速度，并确定长期吸积加热对白色矮星的热影响。了解激变变星中吸积的后果是全面了解整个宇宙中（例如中子星和黑洞周围）与吸积有关的现象的第一步，这些现象不容易观察到。此外，新星爆炸时喷射到星际介质中的物质，以及灾变变星中白色矮星外层的成分，告诉我们哪些元素（金属）有望在星际介质中回收，用于下一代恒星。此外，一些激变变星系统可能是Ia型超新星的祖先，我们对这些吸积白色矮星的理解的变化转化为Ia型超新星产生的可能人口规模的变化。在整个项目中，本科生将在数据的分析和合成光谱建模中发挥关键作用。他们还将通过在专业会议上提交海报文件和共同编写经评审的出版物，参与传播成果。