Performance of the VLT/FORS2 spectropolarimetric mode

"We test the performance of the FOcal Reducer and low dispersion Spectrograph (FORS2) instrument mounted at the Very Large Telescope (VLT), in terms of stability and accuracy, by means of a thorough analysis of archival calibration data of 6 highly linearly polarized and 8 unpolarized standard stars, for a total of 70 epochs. We find a small, but statistically significant, on-axis instrumental polarization wavelength dependency, and provide a re-calibration of a sub-set of highly polarized standard stars that can be very reliably used for technical and scientific purposes (Cikota et al. 2016)."