Our Current Understanding of Classical Be Stars
Dr. Thomas Rivinius, Chile, ESO Paranal
I will introduce Be stars as B-type stars with gaseous disks in Keplerian rotation. These disks form by mass ejection from the star itself and their evolution is then governed by viscosity. The observables and their formation in the disk will be discussed, as well as what we know about the central stars: they are the most rapidly rotating non-degenerate stars, they are non-radial pulsators, and they do not show magnetic fields. The pulsation is clearly (phenomenologically) linked to the mass ejection, but the physical mechanism responsible for the ejection and disk formation is not known. Finally, I will discuss several open questions of broader interest, including the (possibly absent) chemical mixing of very rapid rotators and the unexpectedly large viscosity of Be star disks.
Giant Planet Shielding of the Inner Solar System Revisited: Blending Celestial Mechanics with Advanced Computation
Dr. William Newman, UCLA
The Earth has sustained during the last billion years as many as five catastrophic collisions with asteroids and comets which led to widespread species extinctions. Our own atmosphere was literally blown away 4.5 billion years ago by a collision with a Mars-sized impactor. However, collisions with comets originating in the outer solar system accreted much of the present-day atmosphere. Relatively advanced life on our planet is the beneficiary of a number of impact events during Earth’s history which built our atmosphere without destroying a large fraction of terrestrial life. Using very high precision Monte Carlo integration methods to explore the orbital evolution over hundreds of millions of years followed by the application of celestial mechanical techniques, the presentation will explain directly how Earth was shielded by the combined influence of Jupiter and Saturn, assuring that only 1 in 100,000 potential collisions with the Earth will materialize.