Massive Stars as Cosmic Engines

作为宇宙引擎的大质量恒星

• 批准号: RGPIN-2016-04385
• 负责人: Moffat, Anthony
• 金额: $ 1.97万
• 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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=709280
• 关键词: Massive; Stars; Cosmic; Engines

My research is directed to the determination of the properties of massive stars. Such stars have initial masses above 8 times solar. They eventually fuse elements in successively smaller shells in their cores right through to iron, leading to sudden collapse accompanied by explosion of matter outside the core in the form of a supernova (SN). Although rare, massive stars deliver back to their surroundings far more than their share of radiation and enriched nuclear material for most of their relatively short lifetimes, both from their strong winds and their final SN. This makes them major contributors to the ecology and energetics of the Universe. In this proposal, I will concentrate on the following specific GOALS : (1) Search for and quantify pulsation and rotation properties in luminous massive stars using the recently launched international array of nanosatellites, BRITE-Constellation - a Canadian-driven first in astronomy. Despite their small 30 mm telescopes, all of the five functioning car-battery size BRITE nanosats can obtain precision dual-band photometric time-series (1 mmag rms) of all stars in the sky down to 4-6th magnitude on an hourly basis for up to 6 months. First results from BRITE are already beginning to revolutionize what we know about the properties of massive stars. (2) Recent evidence has revealed that virtually all massive stars form in binaries. In the closer systems, gravitational tidal effects lead to Roche-lobe overflow (RLOF) from one star to the other, actively seen in only a handful of systems. I will carry out a more systematic test of RLOF by quantifying the rotation speeds of O companions in WR+O binaries: the closest systems should have spun-up O-stars from the RLOF process. This effective test will have repercussions in all of stellar astrophysics. (3) Resolve an outstanding fundamental puzzle: dust formation in the hostile radiation fields of hot-star winds. This will be approached in various ways, including zeroing in on the WC9d star WR112 with ALMA in the sub-mm range, and following the Rosetta stone colliding-wind and episodic dust-forming binary WR140 using the CHARA interferometer in the NIR K-band. (4) Continue to search for and quantify the fundamental properties of the most massive stars in the local Universe. This must be done using Kepler's laws in binaries as the only viable method with minimum assumptions. Masses over 100 solar have already been found for the first time in some cases, with more to be examined. Such information is needed to constrain star formation both locally and in the early Universe, where massive stars are believed to dominate. (5) Continue large-scale surveys to locate large numbers of cWR stars (direct descendants of massive H-burning main-sequence stars above 25 solar masses) as immediate progenitors of type Ib/c SNe. Such a direct link has never been made before, yet is required to make progress in understanding the most exotic stellar deaths.

我的研究方向是确定大质量恒星的性质。这类恒星的初始质量高于太阳的8倍。它们最终将核心层中连续更小的壳层中的元素聚变到铁，导致突然坍塌，并伴随着核外物质以超新星(SN)的形式爆炸。虽然很罕见，但大质量恒星在其相对较短的寿命中，无论是从它们的强风还是从它们的最终SN中，向周围传递的辐射和丰富的核材料都远远超过它们所占的份额。这使它们成为宇宙生态和能量学的主要贡献者。在这项建议中，我将重点阐述以下具体目标： (1)利用最近发射的国际纳米卫星阵列BRITE-星座--加拿大推动的天文学第一个--搜索和量化发光大质量恒星的脉动和自转特性。尽管它们有30毫米的小望远镜，但所有五颗功能正常的汽车电池大小的BRITE纳米卫星都可以获得高精度的双波段光度时间序列(1 Mmag RMS)，可以每小时测量一次天空中所有恒星的4-6等，持续长达6个月。首先，来自BRITE的结果已经开始彻底改变我们对大质量恒星的性质的了解。 (2)最近的证据表明，几乎所有的大质量恒星都是在双星中形成的。在较近的星系中，重力潮汐效应导致从一颗恒星到另一颗恒星的罗氏叶溢出(RLOF)，这只在少数几个系统中活跃地看到。我将通过量化WR+O双星中O伴星的自转速度来对RLOF进行更系统的测试：距离最近的系统应该有从RLOF过程中旋转起来的O星。这一有效的测试将在所有恒星天体物理学中产生影响。 (3)解决一个悬而未决的基本难题：热星风敌对辐射场中尘埃的形成。这将以各种方式解决，包括在亚毫米范围内用ALMA对准WC9d恒星WR112，以及在近红外K波段使用查拉干涉仪跟踪Rosetta岩石碰撞风和周期性尘埃形成双星WR140。 (4)继续寻找和量化局部宇宙中质量最大的恒星的基本性质。这必须使用双星中的开普勒定律来完成，因为这是唯一可行的方法，而且假设最少。在某些情况下，已经首次发现了超过100个太阳的质量，还有更多的质量有待研究。无论是在当地还是在早期宇宙中，这些信息都是必要的，以限制恒星的形成，在早期宇宙中，据信大质量恒星占主导地位。 (5)继续进行大规模测量，以确定大量的CWR恒星(25个太阳质量以上的大质量氢燃烧主序恒星的直系后代)是Ib/c SNE类型的直系前身。这种直接的联系以前从未被发现过，但却是在理解最奇异的恒星死亡方面取得进展所必需的。