Multi-Object Spectroscopy

After many years were the MOS mode was used little, it has been requested relatively often over the last few semesters. This has raised a few issues. One is that the machine at the NOT to make the MOS masks was not working properly, and masks are actually made in Copenhagen. Furthermore, the software needed to make the mask design from imaging data is a private copy made by Michael Andersen (NBI, Copenhagen). This has not been a major issue as there were few MOS runs, but this needed to be reviewed given the increased demand.

A review was made of the state of the CNC machine at the NOT that could produce masks on site. It was determined that even if we could repair it and get it to work properly, we do not have the tools or the expertise to maintain it and keep it in working order. One possible option that has arisen is that the TNG has a similar machine to make masks for their own instrument, and a trail run was made of making a copy of an existing mask. Direct comparison of the new and existing mask showed a very good match. The slits produced with the TNG machine were also of good quality, though the width was relatively high (2.9 arcsec). There are still various issues. The material they use is both shiny and thin, i.e., it can not simply be mounted in the ALFOSC slit wheel, while there might be an issue with reflections. The TNG does have a finer tool to make narrower slits, but these would still only be just under 2.0 arcsec wide, while we normally aim for 1.5 arcsec slits on the masks. There are some additional cost involved in making the masks at the TNG.

Some tests were made to determine the distortions in the field of view of ALFOSC which is needed to produce proper mask designs (which requires the specialised software). These tests indicate that this transformation is rather straightforward and could be done without a need for the software.

Our intention is to come to a well defined procedure how masks for a MOS run should be produce, with the specific aim to have everything under direct control on La Palma.