The physical nature of be stars and their circumstellar disks

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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.