new planets in K2

Foreman-Mackey gave the brown-bag talk today. He described the method by which he and Ben Montet (Harvard) and others (including me) have found 20-ish new exoplanets in the K2 data. He is writing up the paper now, and fast (I hope).

The key technology is fitting a model for the systematics simultaneously with fitting the exoplanet transit model, for both search and characterization. This is to be contrasted with "fitting and subtracting" a systematics model prior to search. Fit-and-subtract is very prone to over-fitting; most such systems avoid over-fitting by severely restricting the freedom of the systematics model. If you fit the systematics and exoplanet simultaneously, the systematics will not "over-fit" or reduce the amplitude of the (already weak) exoplanet signals, even if the systematics are given a huge amount of freedom (as we give them). If, furthermore, you marginalize out the systematics (as we do), the method is very conservative with respect to the systematics model and search should be close to optimal (inasmuch as your systematics model is a good model for the data).

The upshot is that they find many exoplanets, multiplying the known yield from K2 by a factor of five, and finding some habitable-zone candidates. Also many eclipsing binaries. Very exciting stuff!

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