Among many other things today, the currently-in-Heidelberg part of the PHAT team (namely Dalcanton, Weisz, Lang, Rix, and Hogg) discussed the first baby steps towards using the young stellar clusters imaged in multiple bands in M31 to measure the stellar initial mass function and its dependence on cluster mass and clustocentric radius. We discussed all the limitations of working at catalog level and also the benefits, and decided to start out with that, with all approaches that are more precise and accurate postponed until we understand all the imaging details better. Lang and I were assigned the task of looking at the information content of the catalogs with respect to radial and mass dependences; Weisz is working on the machinery used for fitting.
Late in the day, Bolton and I discussed spectrograph modeling. My position is that we might be able to vastly improve the accuracy of spectroscopic reductions and high-level science results if we build hierarchical models of the spectrographs, using all the available science and calibration data to infer the parameters. In this vision, the analysis of every exposure would benefit as much as it could from the existence of all the other exposures. We decided that it is too early to embark on this idea; indeed, Bolton was perhaps suspicious that it was even a good idea in the first place.
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