Polarimetry

A few tests were made with the current polarimetry mode available (4 polaroid sheets) observing zero-polarisation standards and high-pol standards, but the results are somewhat inconclusive. It is not clear whether this is due to variable sky, the observing strategy, or the quality of the polaroids (or a mixture). However, with the sequencer it will be possible to cycle through all 4 polaroids per dither position. This is believed to be a better observing strategy. With the sequencer further polarimetry tests will be made and the results will be documented on the web.

It is suggested to upgrade NOTCam with a better mode for linear polarimetry that is 1) more sensitive and 2) less vulnerable to sky transparency variations. Using Wollaston prisms both the ordinary and the extraordinary component (of the orthogonally polarised beams) are obtained in the same exposure and sky transparency variations will cancel out. The requirements, proposed solution and a cost estimate are currently being defined.