[Bicep2-list] BICEP2 polarization angle calibration

Randol, Colin, Walt, Abby: As we discussed again on the telecon today, we *urgently need* final numbers and uncertainties on BICEP2 polarization angle calibrations before - we calculate spectra from our current (maps and see we've "detected" cosmological birefringence, and - we take B2 off the mount and loose the opportunity to ever measure this again. Our target precision for measuring chi's is 0.1 deg. Each of you have worked on this in the past 3 years. But we still don't firm conclusions on what angles to use, or whether uncertainties are anywhere near that precision. We need an immediate plan, so this is what we came up with on the telecon: 1. Walt and Abby will work together to correct the angles derived from the *Jan 2012 RPS data* for the FFFlat pointing model and register them accurately to focal plane coordinates (assuming a reference theta, as usual) for each detector, as Walt began to do in his 20120322 posting <http://bmode.caltech.edu/%7Espuder/analysis_logbook/analysis/20120322_polrot/>. It sounds like they are using Randol's FFFlat pointing model in this. 2. Randol will verify that the chi's derived from *pixel polrasters* by Abby using his code in her 20121112 posting <http://bmode.caltech.edu/%7Espuder/analysis_logbook/analysis/20121112_pxPolvsRPS/> should in principle be properly registered to focal plane coordinates, given reference theta. If not, Randol and Abby work together to please fix this. Goal: check chi's from 1 and 2 agree. (Randol's code is common to both.) 3. Colin will independently use his own FFFlat pointing model to extract properly registered chi's from RPS data, both Jan and Nov 2012. He reported today that he's checked his FFFlat pointing code and Randol's agree on centroids, but unsure whether they agree on angles--this is an important cross-check. Goal: check angles from Jan and Nov 2012 RPS agree. (Basic data quality check, rule out drifts.) Goal: check chi's from 3 and 1 agree. (Check on complicated FFFlat model) Randol, in addition the Yukical data taken in 2010 was analyzed by you in this posting <http://bmode.caltech.edu/%7Espuder/analysis_logbook/analysis/20110302_yukical_reduc/>. You noted in that posting that the Al data looked good, agreed with the model, and could be retaken at any time. Demonstrating agreement between angles derived from that data and from RPS or pixel polraster would be a powerful check (although if we saw systematic disagreement we can imagine explanations). Have you made such a comparison? Is it worth re-taking Yukical data in any case, to compare 2012 vs 2010 Yukical angles? John -- ___________________________________________________________________ John Kovac jmkovac(a)cfa.harvard.edu Assistant Professor, Astronomy and Physics, Harvard University 160 Concord Ave rm 310, Cambridge MA 02138, 617-496-0611