GPRV, day 2

Today was day two of GPRV. It was a delight! Here's another highly unfair summary of the day:

Hara (Geneva) kicked it off with a discussion of a Bayesian-decision-theory-like method for deciding on the reality and correctness of exoplanet discoveries. He made clever choices to deliver really strong probabilistic results. I was about to object to all this but then he disarmed me at the end of the talk by noting that everything is extremely sensitive to noise models and that is the biggest issue. He gave some chilling examples.

Shahaf (Tel Aviv) showed some very nice results in old-school statistics that generalize the periodogram to a correlation between phase differences and distances between pairs of any quantities you like, as a function of period. This can be used to perform causal inferences for periods seen in naive periodograms. He uses a very interesting phase variable for these phase differences; this is extremely relevant to things I have been discussing with Zhao and Bedell.

Mortier (Cambridge) mesmerized the room with her work with six (yes 6) years of solar data from HARPS-N (maybe). She can show amazing relationships between pipeline RVs, activity indicators, and spectral shape measures. But she showed that often the correlations are not at zero-time-lag. Often the correlations are strongest with delays of 1/9 to 1/8 of a rotation period. When she sub-samples the data to typical kinds of long-term monitoring campaigns we are going to do on distant stars, it is a bit scary. That led to a lot of discussion over lunch and dinner.

Zhao (Flatiron), Bucchave (DTU), and Dumusque (Geneva) led discussions on community-building, hardware, instrument calibration, and other things. The meeting is set up for lots of discussion and is itself an extremely good example of a community-building activity, around the hard challenges of EPRV. I opined in one of these sessions that EPRV now looks like cosmology around 2000, when everything was just about to go open and the world community started working together. This meeting is part of this change that we want to see.

Finally, a theme of the day was representations for spectral signals. Dumusque (inadvertently, I think) made a strong case that we should be working in the 2-d spectrograph images directly! That's music to my heart. He also emphasized that the stellar surface is a complex physical place. I agree! And Cretignier (Geneva) showed a beautiful representation of the spectral residuals to disentangle Doppler and spectral-variability variations. I think his work and Shahaf's could be combined in interesting ways; I am excited to get back to the lab.