Asteroseismology, Cosmochronology, Planetology, and Stellar Evolution at the Bottom of the HR Diagram

HR 图底部的星震学、宇宙年代学、行星学和恒星演化

• 批准号: RGPIN-2014-04986
• 负责人: Fontaine, Gilles
• 金额: $ 4.3万
• 依托单位: Université de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=588140
• 关键词: Asteroseismology; Cosmochronology; Planetology; Stellar; Evolution

This proposal is about a research program aimed, in part, at further exploiting the unique properties of white dwarf stars. As the final products of stellar evolution for the vast majority of stars, white dwarfs bear the signature of past events of fundamental importance in stellar life: mass loss, phases of convective mixing, loss and redistribution of angular momentum, thermonuclear burning. They are also ideal cosmic laboratories for testing our theories of matter under extreme conditions of pressure and temperature. White dwarfs may also be used as cosmochronometers and distance indicators for the different components of the Galaxy (disk, halo, open and globular clusters). Recently, planetary debris have been identified at the surface of several white dwarfs, which has led to the exciting possibility of determining in a unique and novel way the *bulk* composition of these ancient planets. To decipher the information contained in white dwarfs, which, in many ways, behave as "fossils" of stellar evolution, researchers in the field dispose of powerful tools based on model atmosphere theory, stellar evolution theory, and stellar pulsation theory. In the latter case, Nature has chosen to cooperate with us since no less than 6 distinct types of pulsating white dwarfs -- each corresponding to a different evolutionary phase -- are now known, including the recent discoveries of two new types in 2012 and 2013. Asteroseismology can be used to determine, among other things, the internal chemical layering of white dwarfs (core composition and envelope chemical stratification), which is an essential input in cooling calculations. Hence, white dwarf asteroseismology may be used to "calibrate", so to speak, the internal chemical structure, a step necessary for exploiting fully the cosmochronological potential of these stars. This proposal is also concerned with another category of evolved and compact stars, the hot subdwarfs, whose origin is still being debated. They constitute a sort of "gray zone" in the grand scheme of stellar evolution and, as such, their very existence represents a challenge for those interested in stellar evolution theory. It is known that hot subdwarfs are former red giant stars and that their destiny is to become low-mass white dwarfs, but the details of their formation process are still uncertain. A number of competing formation scenarios have been proposed, some involving binary evolution (common envelope evolution, Roche lobe overflow, mergers), others single star evolution (with peculiar mass loss rates in the red giant phase). It has been proposed recently that planets orbiting around "isolated" hot subdwarfs (i.e., not part of binary systems) may provide the necessary "kick" needed to expel extra mass in the red giant phase. And planets have been detected around hot subdwarfs. One of the long-term goals of this proposal is to discriminate between the various formation scenarios that have been proposed for hot subdwarfs. This can best be done by deriving the empirical mass distribution of these stars, which bears the signature of the actual formation process. Unfortunately, reliable mass estimates for these stars coming from the standard methods are far and few. For instance, spectroscopic masses are notoriously uncertain for hot subdwarfs. However, the powerful method of asteroseismology can again come to the rescue as Nature has provided us with no less than 4 different types of pulsating hot subdwarfs (first type discovered in 1997, and the newest one in 2011). In fact, the pulsating hot subdwarfs have turned out to be the best asteroseismological tesbeds that currently exist, and masses, along with many other properties, can be determined both accurately and precisely for these stars.

这项提议是关于一项研究计划，其部分目的是进一步利用白色矮星的独特性质。作为绝大多数恒星演化的最终产物，白色矮星具有恒星生命中过去重要事件的特征：质量损失，对流混合阶段，角动量的损失和重新分配，热核燃烧。它们也是在极端压力和温度条件下测试我们的物质理论的理想宇宙实验室。白色矮星也可以作为宇宙计时器和距离指示器，用于银河系的不同组成部分（盘，晕，疏散星团和球状星团）。最近，在几颗白色矮星的表面发现了行星碎片，这导致了令人兴奋的 以一种独特而新颖的方式确定这些古老行星的组成的可能性。 为了破译白色矮星中包含的信息，在许多方面，白矮星表现为恒星演化的“化石”， 基于模式大气理论、恒星演化理论和恒星脉动理论的强有力的工具。在后一 在这种情况下，大自然选择与我们合作，因为不少于6种不同类型的脉动白色矮星-每一种都对应一个 不同的进化阶段，包括最近在2012年和2013年发现的两种新类型。除其他外，天文地震学还可用于确定白色矮星的内部化学分层（核心成分和包层化学成分 分层），这是冷却计算中的基本输入。因此，白色矮星震学可以用来“校准”，可以这么说，内部化学结构，充分利用这些恒星的宇宙年代学潜力的必要步骤。 这一提议还涉及另一类演化的致密恒星，即热亚矮星，其起源仍在争论中。它们在恒星演化的宏伟计划中构成了一种“灰色地带”，因此，它们的存在对那些对恒星演化理论感兴趣的人来说是一个挑战。我们知道，热的次矮星是以前的红巨星，它们的命运是变成低质量的白色矮星，但它们形成过程的细节仍然不确定。一些竞争的形成方案已经提出，一些涉及双演化（共同的信封演变，罗氏瓣溢出，合并），其他单星星演化（在红巨星阶段的特殊质量损失率）。最近有人提出，围绕“孤立的”热亚矮星（即，不是双星系统的一部分）可能提供必要的“反冲”，需要驱逐红巨星阶段的额外质量。在炽热的次矮星周围发现了行星。 这个提议的长期目标之一是区分已经提出的热亚矮星的各种形成方案。这可以通过推导这些恒星的经验质量分布来最好地完成，它带有实际形成过程的签名。不幸的是，通过标准方法对这些恒星的质量进行可靠的估计是非常少的。例如，众所周知，热亚矮星的光谱质量是不确定的。然而，强大的星震学方法可以再次拯救我们，因为大自然已经为我们提供了不少于4种不同类型的脉动热次矮星（第一种类型于1997年发现，最新的一种在2011年发现）。事实上，脉动炽热的次矮星已被证明是目前存在的最好的星震学实验场，质量以及沿着许多其他性质都可以准确而精确地确定。