| | 8 | We had a somewhat abbreviated week with the holiday on Friday and a power outage in Manoa on Wednesday. I spent much of the week working on issues related to astrometry and proper motion measurements. I defined a new DVO format to support additional fields in the average position table needed to check on the quality of the proper motion measurement. I adjusted 'relastro' so that all objects which are fitted for proper motion are also fitted for a static position, and the chisq from both fits are saved in the database. I also added flags to track which fits had been tested and which fit was kept. I also realized that the position errors from the proper motion fit are coupled to the velocity errors, so that the reported errors are amplified if the reference epoch is far from the fitted time range. Previously, I had been fitting with a reference epoch of J2000 in all cases, but this gives odd results for PS1-only proper motion fits. For example, if we fit proper motion to the years 2009 and 2010 referenced to 2000, the error on the mean position include the nominal mean position (say, 15 mas) plus the nominal velocity errors (say 15mas/year) times the extrapolation (10 years). Although one could back out these correlations, I decided it would makes like easier to perform the fit relative to the mean epoch. That in turn requires the database to track the mean epoch. |
