Determine whether scaling the non-z′ modulator-efficiency corrections improves accuracy

Determine whether applying additional scale factors to the PICSARR-2 modulator-efficiency corrections in bands other than the z′ band produces greater polarimetric accuracy and agreement with standard-star measurements.

Background

PICSARR-2 calibrates its polarization measurements using a wavelength-dependent model of the half-waveplate modulator efficiency. The authors compare measured polarizations of standard stars with values predicted from an established bandpass model and find substantial scatter in the literature polarization values of the standards.

The z′-band measurements differ significantly from the model prediction, leading the authors to apply a scale factor of 1.0721 in that band. They note that similar rescaling could be applied to the other passbands, but the available evidence does not establish whether doing so would improve rather than degrade the resulting accuracy. Thus, the unresolved issue is whether additional band-specific corrections are justified for the non-z′ bands.