source detection, Pal 5

In the early morning, I not only fixed all the bugs I created yesterday, but I also worked out some fundamental issues with doing source detection in images with very limited dynamic range, like jpegs off the web and scans of photographic plates. These issues are obvious, but non-trivial: Stars have to be subject to strong non-linearities, and at the bright end, it is the size of the source that is related to flux, not the peak value in the image (which has saturated). Of course these issues are known. What is not known is what to do, in general, in data of which you have little or no knowledge, and when extended sources can be as prevalent as stars. These are the conditions under which astrometry.net operates! Blanton helped me come up with some ideas.

In the late morning and afternoon, Kallivayalil and I agreed to focus on getting a proper motion for Pal 5. This is a project that is hard, but not impossible (we hope), and finite. The first step is to gather all the HST data, survey data, plate data, and random ground-based data that we can find, and to turn those data into precise coordinate lists.

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