PCA, hst pixels

Long discussions today between Sandstrom (MPIA), Groves (MPIA), Kapala (MPIA), Weisz (UW) and me about inferring the total mean intensity from a patch of the sky from the pixel photon counts in a large patch of HST imaging. I think the problem is hard enough—given zodiacal, Galactic, and extragalactic backgrounds (well the first two I guess are foregrounds)—without the additional problem that we don't understand the HST pipeline processing. I got even more upset about the idea (encoded in DrizzlePac) that images are grids of buckets of photons; this view leads to ideas like "transformations that preserve flux" (when in fact transformations should preserve intensity), and makes all interpretation extremely sensitive to pixel solid angles, which may or may not be properly multiplied in (with an intensity image, failure to multiply in would be failure to calibrate; not so when you are just counting photons).

Collaborator Tsalmantza was shocked to hear me talking about PCA with the exoplanet direct imaging group (headed by Brandner) since I have devoted quite a bit of my last few years attacking PCA. I guess I now have to agree that PCA is sometimes useful. It is never Mr Right but it is sometimes Mr Right Now. Everyone in the direct imaging world is talking PCA right now, I think in part because we have all reached the limit of what means can teach us. In Brandner's group meeting we also talked about finding young M stars, which are great exoplanet search targets because they are not so luminous and when young the planets might still be hot. Young M stars have activity that give them line, UV, and X-ray emission; the planets might too; that seems like an interesting thing to think about!