Polarimetry

Polarimetry measurements were taken with FAPOL in the B and R filter of the standard stars and candidate standard stars currently investigated with TurPol in order to find the relative calibration between these two instruments. We also took repeated zero-polarization standards at various rotator positions and with many retarder angles to check for any systematic effects and check if the accuracy can be improved. These data are being analyzed.

The ALFOSC calcite plates (one open, one with slit) were rotated 90 degrees and aligned in order to save overheads when doing (high time resolution) spectro-polarimetry. In this way the readout time for the typical spectro-polarimetry windowing went down from 40s to 13s. These changes have been tested and documented.

At some moment there was some confusion on which retarder plate was installed in FAPOL. To make this more visible, the name of the mounted retarder plate is now displayed on the FAPOL status window.

The quick-look data reduction tool for linear polarimetry will be further developed to allow for the analysis of data with a different number of retarder plate angles (4, 8 or 16) and/or a different set of angles (e.g., using 90$^{\circ}$, 112.5$^{\circ}$, 135$^{\circ}$, and 157.5$^{\circ}$, instead of 0$^{\circ}$, 22.5$^{\circ}$, 45$^{\circ}$, and 67.5$^{\circ}$). The analysis of the data will also be added as part of the automatic post-processing of the data.

No progress has been made with the Wedged double Wollaston that would be purchased by astronomers from the Instituto de Astrofísica de Andalucía and from the DARK institute in Copenhagen to do linear polarimetry with ALFOSC.