On the third day of Telluric Line Hack Week, I had many great conversations, especially with co-organizer Cullen Blake (Penn), who has had many astronomical interests in his career and is currently building the CCD part of the near-future NEID spectrograph. In many ways my most productive conversation of the day was with Mathias Zechmeister (Göttingen) about how we combine the individual-order radial-velocity measurements with wobble into one combined RV measurement. He asked me detailed questions about our assumptions, which got me thinking about the more general question. Two comments: The first is that we officially don't believe that there is an observable absolute RV. Only relative RVs exist (okay, that's a bit strong, but it's my official position). The second is that once you realize that you will be inconsistent (slightly) from order to order, you realize that you might be inconsistent (slightly) on all sorts of different axes. Thus, the RV combination is really self-calibration of radial-velocity measurements. If we re-cast it in that form, we can do all sorts of new things, including accept data from other spectrographs, account for biases that are a function of weather, airmass, JD, or barycentric correction, and so on. Good idea!
Despite the workshop, we still held the weekly Stars Meeting at Flatiron, and I am sure glad we did! Sharon X Wang (DTM) gave a summary of what we are doing at #tellurics, Dan Tamayo (Princeton) told us about super-principled numerical integrations that are custom-built for reproducibility (which is crazy hard when you are doing problems that are strongly chaotic), and Simon J Murphy (Sydney) told us about a crazy binary star system with hot, spotty stars. The conversation in the meeting pleased me: These meetings are discussions, not seminars. The crowd loves the engineering, computing, and data-analysis aspects to the matters that arise and we are detail-oriented!
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