better photometry for Kepler

Because Hou has finished and submitted his paper on the (apparently aptly named) FML, today's MCMC meeting devolved into a discussion of how Kepler does its simple aperture photometry (or SAP, if you like the acronym circus). By the end of the meeting, we had formulated a question in fundamental astronomy which I am not sure has been answered in the literature: If you know your point-spread function (PSF or pixel-response function or PRF or pixel-convolved point-spread function or PCPSF) perfectly but you have a pointing jitter, such that each exposure is not at precisely the same pointing, with what method or weights should you "co-add" your pixel values to get the most consistent possible photometry from exposure to exposure? The rules are that you aren't permitted to re-centroid the star in every frame; you have to do the same operation on every frame. There are only five people on this Earth who have ever wanted to know the answer to this question, but it now turns out that I am one of them.

In FML news, we asked Hou to see if we can compute the FML for exoplanet models in the Kepler data, even for target stars that don't have any high-significance planet transits. That, we anticipate, will be a very hard problem to solve.


  1. The goal to find out the best weights to co-add the pixels would be to achieve the lowest SNR. But I feel the current SNR is somewhat arbitrarily defined.

    1. We should make a non-arbitrary definition and solve that problem.