The physical nature of be stars and their circumstellar disks

旋转或“自旋”在宇宙中无处不在。地球、太阳和银河系都在旋转。所有这些物体都是由大爆炸后的引力坍缩形成的，这种坍缩自然地增加了任何初始的小的、随机的旋转。一个有趣的问题是，这种自转是如何塑造恒星、行星和星系的生命的。天文学家知道，快速自转可能是质量超过太阳三倍的恒星演化的关键因素。虽然这样的恒星比太阳质量的恒星要少，但它们为银河系的星际介质（新恒星的形成）提供了大部分的能量和质量，并且它们（通过核燃烧和超新星爆炸）合成了生命所必需的所有化学元素。然而，对旋转在大质量恒星的生命中所起的作用的连贯理解还远远没有完成。我的研究将聚焦于旋转速度最快的核心氢燃烧恒星，即B型发射线或Be型恒星，以此来解决这个问题。这些恒星的自转周期大约是一天（相比之下，我们的太阳大约是一个月），而且它们的赤道周围有一个气体盘。然而，Be恒星的旋转速率是高度不确定的，快速旋转在形成它们的圆盘中所起的作用是未知的。我将使用新的计算技术，以及新的观测结果，其中一些是在加拿大-法国-夏威夷望远镜获得的，以准确估计Be恒星旋转的速度。任何关于它们的圆盘如何形成的模型都必须与这些旋转速率相一致。我还将尝试探测这些恒星大气中元素丰度的模式，以找到由快速旋转驱动的Be恒星内部混合的第一个证据。这将对大质量恒星的旋转演化提出重要的新限制，并可能有助于理解宇宙中的奇异事件，比如伽马射线爆发，它被认为是由最巨大、最快速旋转的恒星的超新星爆炸形成的。加拿大作为一个整体将受益于这项研究，通过研究生训练的高性能计算和数据可视化需要完成这些研究项目。

Rotation, or "spin," is ubiquitous in the Universe. The Earth, the Sun, and the Milky Way Galaxy all rotate. All of these objects formed from gravitational collapse after the Big Bang, and this collapse acts naturally to increase any initial small, random rotation. An intriguing question is how this rotation shapes the lives of stars, planets, and galaxies. Astronomers know that rapid rotation can be a key element in the evolution of stars more massive than about three times the mass of the Sun. While such stars are rarer than solar-mass stars, they supply most of energy and mass to the interstellar medium of the Milky Way (out of which new stars form), and they synthesize (through nuclear burning and supernova explosions) all of the chemical elements essential for life. However a coherent understanding of the role rotation plays in the lives of massive stars is far from complete. My research will address this problem by focusing on the most rapidly rotating, core hydrogen burning stars, the B emission-line or Be stars. Be stars rotate with periods of about one day (compared to about one month for our Sun), and they are known to possess a disk of gas surrounding their equator. However, rotation rates for Be stars are highly uncertain, and the role that rapid rotation plays in forming their disks is unknown. I will use new computational techniques, along with new observations, some obtained at the Canada-France-Hawaii Telescope, to accurately estimate how fast Be stars rotate. Any model of how their disks form will have to be consistent with these rotation rates. I will also attempt to detect patterns in the abundances of the elements in the atmospheres of these stars to find the first evidence for internal mixing in Be stars driven by their rapid rotation. This will place important new constraints on the rotational evolution of massive stars and will potentially help to understand exotic events in the universe, such as gamma-ray bursts which are though to form from the supernova explosions of the most massive, rapidly rotating stars. Canada as a whole will benefit from this research through the graduate students trained in high-performance computation and data visualization required to complete these research projects.