Evolution of helium-accreting carbon-oxygen white dwarfs towards helium-detonations

人们认为，吸积白矮星中的热核爆炸是宇宙中许多发光瞬变的原因，包括Ia型超新星，它是精密宇宙学和宇宙化学演化的重要对象。最近，CO白矮星中高度简并的氦壳层的爆炸被认为是Ia型超新星和某些特殊的Ib型超新星的一种可能的机制。氦爆炸的可观察结果敏感地取决于氦壳体点火时的热力学条件。这个项目将系统地探索近双星系统中吸氦的CO白矮星的演化，以预测宇宙中通过氦爆炸发生的爆炸类型。继我们之前关于自转对吸积白矮星演化影响的研究之后，我们将首先研究所谓的Spruit-Tayler发电机产生的磁矩对吸氦白矮星演化的影响及其对氦爆超新星爆炸的意义。我们将特别关注白矮星中由质量和角动量吸积形成的差动旋转层中摩擦加热的后果，以及旋转诱导的化学混合。随后，我们将计算自洽双星演化模型，以研究近双星系统中依赖时间的质量传递是否会导致双星轨道的合并或重大变化，从而影响系统的最终命运。通过这些研究，我们将能够为氦爆炸产生现实的前驱模型，并解决以下问题：大多数普通的SNE Ia是否可以通过氦爆炸产生，哪些其他瞬变(氦新星、特殊的SneIa或特殊的SneIb)可能不是这样的，以及核合成将产生什么后果。

It is believed that thermonuclear explosions in accreting white dwarfs are responsible for many luminous transients in the Universe, including Type Ia supernovae that are important objects for the precision cosmology and for the chemical evolution of the universe. Recently, detonations of the highly degenerate helium shell in a CO white dwarf that slowly accretes helium-rich matter has been proposed as a possible mechanism for Type Ia supernovae as well as for some peculiar Type Ib supernovae. The observable outcomes of a helium detonation sensitively depends on the thermodynamic conditions of the helium shell when it ignites. This project will systematically explore the evolution of helium-accreting CO white dwarfs in close binary systems, to predict which types of explosion would occur via helium detonation in the universe. Following-up our previous studies on the effects of rotation on the evolution of accreting white dwarfs, we will first investigate the effects of magnetic torques due to the so-called Spruit-Tayler dynamo on the evolution of helium-accreting white dwarfs and its implications for supernova explosions induced by helium detonations. Particular attention will be given to the consequences of frictional heating in differentially rotating layers in white dwarfs that are spun-up by mass and angular momentum accretion, and to rotationally induced chemical mixing. Following this, we will calculate self-consistent binary star evolution models to investigate whether time-dependent mass transfer in a close binary system would lead to a merger or significant change of the binary orbit, so as to affect the final fate of the system. With these studies, we will be able to produce realistic progenitor models for helium detonations, and to address the questions whether the majority of ordinary SNe Ia can be produced via helium detonations, which other transients (helium novae, peculiar SNe Ia, or peculiar SNe Ib) would be expected otherwise, and what would be the consequences for nucleosynthesis.