Spectroscopy

A new script was made to allow making automatic ALFOSC spectroscopy calibration scripts. The script has a hard-coded version of the table we provide with standard exposure times for different combinations of grism and calibration lamp(s). The new script returns the exposure time that can be fed to an exposure command or script. The script can optionally account for binning and the slit width. The latter only for Halogen lamp (flat field) exposures, as line strengths from wavelength calibration lamps are in general not affected by the slit width. We are still working on a more sophisticated script that will take a test exposure for any combination of grism, lamp(s) and slit width, and based on the result subsequently take a properly exposed calibration exposure.

When acquiring a target with the slit acquisition script using the slit view option, one sometimes want to do a small telescope offset to center the star better, but then you would like to take an other through slit image to check. This latter option was added to the script. The acquisition script was also streamlined for the (spectro)polarimetry mode using FAPOL. In this mode no automatic rotation of the displayed acquisition image to have North up is made, as this complicates the recognition of the ordinary and extraordinary components. We are investigating how to further streamline the target-acquisition process by analysing the typical offset done after the initial pointing of the telescope to the target, possibly making a first automated telescope offset before doing a more time-consuming interactive on-slit acquisition.

In relation to the fixed set-up requested by the different Target-of-Opportunity programs that can use the NOT at any time, it was mentioned that the 10 arcsec slit is part of the fixed set-up (for use with the Wedged-Double-Wollaston to do imaging polarimetry) while regular programs often request the 5 arcsec slit, which sometimes generates conflicts. There seems no specific difference or advantage for spectroscopic observations in using the 5 arcsec slit instead of the 10 arcsec slit, and it was suggested to decommission the 5 arcsec slit. It will be checked if there is any reason not to do so, and if not, the 5 arcsec slit will be removed from the available set-up.