binary stars and lots more

Today was a very very special Stars meeting, at least from my perspective! I won't do it justice. Carles Badenes (Pitt) led us off with a discussion of how much needs to be done to get a complete picture of binary stars and their evolution. It's a lot! And a lot of the ideas here are very causal. For example: If you find that the binary fraction varies with metallicity, what does it really vary with? Since, after all, stellar age varies with metallicity, as do all the specific abundance ratios. And also star-formation environment! It will take lots of data and theory combined to answer these questions.

Andreas Flörs (ESO) spoke about the problem of fitting models to the nebular phase of late-time supernovae, where you want to see the different elements in emission and figure out what's being produced and decaying. The problem is: There are many un-modeled ions and the fits to the data are technically bad! How to fix this. We discussed Gaussian-process fixes, both stationary and non-stationary. And also model elaboration. And the connection between these two!

Helmer Koppelman (Kapteyn) showed some amazing structure in the overlap of ESA Gaia data and various spectroscopic surveys (including LAMOST and APOGEE and others). He was showing visualizations in the z-max vs azimuthal-action plane. We discussed any ways it could be selection effects. It could be; it is always dangerous to plot the data in derived (rather than more closely observational) properties.

Tyson Littenberg (NASA Marshall) told us about white-dwarf–white-dwarf (see what I did with dashes there?) binaries in ESA LISA. He has performed an information-theoretic analysis for a realistic Milky Way simulation. He showed that many binaries will be very well localized; many thousands will be clearly detected; and some will get full 6-d kinematics because the chirp mass will be visible. Of course there are simplifying assumptions about the binary environments and accelerations, but there is no doubt that it will be incredible. Late in the day we discussed how you might model all the sea of sources that aren't individually detectable. But that said, everything to many tens of kpc in the MW will be visible, so incompleteness isn't a problem until you get seriously extragalactic. Amazing!