In order for a white dwarf (WD) to achieve the Chandrasekhar mass, M_C, and explode as a Type Ia supernova (SNIa), it must interact with another star, either accreting matter from or merging with it. The failure to identify the types of binaries which produce SNeIa is the "progenitor problem". Its solution is required if we are to utilize the full potential of SNeIa to elucidate basic cosmological and physical principles. In single-degenerate models, a WD accretes and burns matter at high rates. Nuclear-burning WDs (NBWDs) with mass close to M_C are hot and luminous, potentially detectable as supersoft x-ray sources (SSSs). In previous work we showed that > 90-99% of the required number of progenitors do not appear as SSSs during most of the crucial phase of mass increase. The obvious implication is that double-degenerate (DD) binaries form the main class of progenitors. We show in this paper, however, that many binaries that later become DDs must pass through a long-lived NBWD phase during which they are potentially detectable as SSSs. The paucity of SSSs is therefore not a strong argument in favor of DD models. Those NBWDs that are the progenitors of DD binaries are likely to appear as symbiotic binaries for intervals > 10^6 years. In fact, symbiotic pre-DDs should be common, whether or not the WDs eventually produce SNeIa. The key to solving the progenitor problem lies in understanding the appearance of NBWDs. Most do not appear as SSSs most of the time. We therefore consider the evolution of NBWDs to address the question of what their appearance may be and how we can hope to detect them.
PTF11kx: A Type-Ia Supernova with a Symbiotic Nova Progenitor
有一个共识是Ia型超新星（SNe Ia）是由白矮星的热核爆炸产生的，它从一个双星伴星中吸积了物质。然而，对Ia型超新星前身的直接观测仍然缺乏，而这颗双星伴星的确切性质仍然不确定。SN Ia PTF 11kx的高分辨率光谱的时间序列揭示了一个复杂的星周环境，提供了一个前所未有的详细的祖系统。多个壳的circumsteller检测和SN喷出物被认为是相互作用的circumsteller材料（CSM）开始后59天爆炸。这些特征最好由一个共生的新星祖先来描述，类似于RS蛇夫座。
Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors -- II. Type II-P and II-L supernovae
利用积分场光谱学已经观测到了附近星系中II-P和II-L型超新星的13个爆炸点，使得对爆炸点的空间和光谱研究成为可能。我们利用同时代超新星祖先星的母恒星星族的性质来推导它的金属丰度和初始质量（c.f. Paper I）。母恒星星族的光谱通过强线方法得到金属丰度的估计，并通过与简单的恒星星族（SSP）模型的比较得到年龄。这些金属丰度和年龄参数被采用的祖星。通过与恒星演化模型的比较，利用恒星的年龄或寿命来推导恒星的初始质量。利用这种技术，我们能够确定我们样品中SN祖细胞的金属丰度和初始质量。我们的结果表明，一些II型超新星的祖先可能是质量与SN Ib/c祖先相当的恒星。
