Many great things happened at the meeting today; way too many to mention. Steinmetz showed how good the RAVE-on results are, and nicely described also their limitations. Korn showed an example of an extremely underluminous star, and discussed possible explanations (most of them boring data issues). Brown explained that with a Gaia mission extension, the parameter inference for exoplanet orbit parameters can improve as a huge power (like 4.5?) of mission lifetime. That deserves more thought. Gerhard explained that the MW bar is a large fraction of the mass of the entire disk! Helmi showed plausible halo substructure and got me really excited about getting ready for Gaia DR2. In the questions after her talk, Binney claimed that galaxy halos don't grow primarily by mergers, not even in theory! Hobbs talked about a mission concept for a post-Gaia NIR mission (which would be incredible). He pointed out that the reference frame and stellar positions require constant maintenance; the precision of Gaia doesn't last.
One slightly (and embarrassingly) frustrating thing about the talks today was that multiple discussed open clusters without noting that we found a lot ourselves. And several discussed the local standard of rest without mentioning our value. Now of course I (officially) don't mind; neither of these are top scientific objectives for me (I don't even think the LSR exists). But it is a Zen-like reminder not to be attached to material things (like citations)!
To clarify the t^4.5 improvement mentioned in my talk: this concerns unseen companions to stars with an orbital period much larger than the mission lifetime. It turns out that if you want to unambiguously identify the period, mass, and distance of the unseen companion it is not enough to measure the acceleration, as this can be due to a close low mass companion or a distant massive one. The third derivative of time is degenerate with the system proper motion. Measuring the fourth derivative of time allows to partly resolve this degeneracy. Hence the t^4.5 improvement for long period systems.
ReplyDeleteIn general this illustrates how the doubling of the Gaia mission lifetime dramatically improves the interpretation of complex objects observed by Gaia.
This insight was contributed by Lennart during the discussions on the science case for a Gaia mission extension.