Spectroscopy

With the change in the dewar the instrument focus had to be redetermine, both for normal spectroscopy and for spectro-polarimetry. The target acquisition script was adapted to work with the data from the new CCD controller. It was also upgraded to check for the telescope focus in case no filter is used during the acquisition, while the instrument focus (either for normal use or for polarimetry) is now read from the data-base such that it automatically checks for the correct value even if these values change.

One thing noted with the use of the target acquisition script is that it is still a relatively slow process. This is largely defined by the need to do more than one iterative step to get a star well centered. The first step typically involves an offset in the order of 10-20 arcsec as the center of the slits do not coincide with the pointing center. As the resulting offset typically has an error of a few percent (a few 0.1 arcsecs) a second iteration is needed in basically all cases. Given accurate coordinates, in principle one would expect the overall offset to be the same for all objects and it should be possible to record this offset and apply it as part of the acquisition script removing the need for the first iterative step. However, it is not entirely clear if these offsets are indeed the $\sim$same in all cases and how this applies when using different field-rotation angle and/or a fixed rotator angle (e.g., when pointing using the parallactic angle). To test this, a logging feature was added to the ``alfosc.acquisition'' script that records the accumulated offsets (both in RA & Dec, and in X & Y detector pixels) together with several relevant instrument and telescope parameters.

The grism holders of the low resolution ``cross-disperser'' grisms #10-12 where modified such that they can be mounted in both the grism and filter wheel without having to rotate the grisms in their mounting ring.

There was some confusion about the correct procedure to align the slits and grisms in ALFOSC and the instructions for the staff were updated and clarified.