My day started (at 07:00) with a call with Neige Frankel (CITA) and Scott Tremaine (IAS) about our project to understand the phase-space spiral in the vertical kinematics of the disk in terms of metallicity, element abundances, stellar ages, and so on. Indeed, we have a general argument that any non-equilibrium perturbation of the Galaxy, winding up into a spiral, will show a metallicity (or other stellar-label) effect, provided that there were gradients in the metallicity (or other label) with respect to stellar density, or phase-space density, or orbital actions. The argument is exceedingly general; I want to write a paper with wide scope. Tremaine is careful with his conclusions; he wants to write a paper with narrow scope. We argued. The data (compiled and visualized very cleverly by Frankel) are beautiful.
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