how to measure proper motions

Bovy and I discussed how we are going to measure proper motions from SDSS-III imaging (and SDSS-I and SDSS-II imaging) in comparison with USNO-B imaging. We want to model the pixels, but pragmatic considerations may force us to execute only a rough approximation to that lofty goal.

proper motion measurements

Among other things, Bovy and I discussed the first steps towards measuring proper motions in the USNO-B and SDSS raw data streams. This is a big project, but we have decided to get closer to the data.

astrometric verification

The Astrometry.net system works by generating likely hypotheses about each input image's astrometric calibration, and then testing those hypotheses with a verification process, which we have cast as a well-posed statistics problem in the formalism of Bayesian hypothesis testing. If we have this right, then the false-positive rate (which we want to have vanishingly small) is an explicit parameter in our system, not implicitly set by ad-hoc cuts or thresholds.

Unfortunately, our false-positive rate is orders of magnitude higher than it should be. This is because our well-posed statistics problem is an approximation to the problem we really need to solve. In detail, to do it right, we would need a generative model of the USNO-B Catalog (our basis for truth), the sky, and all sources of astronomical imaging. We are far from this, so we have to make approximations. Today Lang and I spent all day trying to improve our approximation. We didn't finish, but we learned a lot.

GALEX and 2MASS, Spitzer IRS

Schiminovich and I re-tooled our GALEX–USNO project (build an all-sky quasar catalog, using the SDSS as a training set) into a GALEX–2MASS project. It appears that the 2MASS photometry is better suited to our purposes, although the 2MASS source density is not as high.

Schiminovich, Wu, and I looked at the pixel level at Spitzer IRS spectra. There are some very strange things in the statistical properties of the sky frames that we don't understand. But it appears that we may be able to do science without fully understanding this.

GALEX and USNO-B

Schiminovich and I got our plan off the ground to look at an all-sky catalog built from GALEX and USNO-B data. So far, it doesn't look pretty, but I am hoping that is a bug in my code, and not the photometric issues with USNO-B.

USNO-B and GALEX, supervised

I got stranded in Nantucket by high winds (cancelled ferries). This cost me Monday, and I spent parts of today making up for it. My research time was spent with Schiminovich, talking about what we should do with the SDSS and GALEX, and what we will do in the very short term. The very short term project is to use SDSS and GALEX to learn what quasars look like and then find them all-sky with USNO-B1.0 and GALEX. Same with white dwarfs. This is a nice project in supervised methods for automated classification, something I was railing against in Ringberg.

USNO-B and 2MASS

Lang and I conceived of and started to work out a project to build an all-sky astrometric catalog out of the original USNO-B imaging catalogs and the 2MASS catalog, all tied to Tycho. This would be the first step towards our first Astrometry.net astrometric catalog. This would also be a first shot at doing source matching at the catalog level, a subject about which we have been talking for half a year. The first order of business, we realized, is to make a conceptual data model and a scalar objective function.