the bulge

In a low-research day, Melissa Ness (MPIA) led a discussion in the Milky Way group meeting about the Milky Way Bulge. She showed that it very clearly has an x-shape (peanut-shape or boxy shape) and that the x-shape is more visible in the higher metallicity stars. She also showed evidence from simulations that the higher metallicity stars are more represented in the x-shape because of the phase-space distribution they had when they were excited into the x-shape orbits by the bar; that is, the metallicity distribution in the bulge is set by the excitation mechanism as much as the properties of the star formation. One thing that was interesting to me about this is that the bulge is x-shaped and the orbits are also x-shaped. That means that maybe we could just "read off" the orbits from the three-dimensional distribution of stars. Ish. That's not often true in dynamical systems. Ness's data come from a sparse sampling of the sky, but her results are about big, continuous structures. It would be great to get complete (meaning spatially contiguous) coverage (meaning spectral observations) of giant stars all over the bulge!