Atmospheric dispersion corrector

As of December 2010 we have the ADC on offer for regular use. The ADC can be used to minimise the wavelength-dependent fiber-aperture losses that are due to the atmospheric dispersion at large zenith distances. The ADC swings into the telescope beam before the FIES/STANCAM pickoff mirrors, and provides an unvignetted field of view of about 3 arc-minutes. The ADC consists of a set of two rotating prisms, that together compensate for the atmospheric effect. The ADC was primarily designed for use with FIES, but can be also be used with ALFOSC or NOTCAM. For use with FIES the ADC is expected to be advantageous in terms of throughput and radial-velocity precision for sources at high ($\ge$1.5) airmass.

The general use of the ADC has been documented on the web-pages providing commissioning results and a concise user guide. Sequencer commands to operate the ADC were implemented and were added to the list of available commands. The status of the ADC has been integrated in the FIES status display and added to the FITS keywords. The telescope setup scripts for the various instruments have been modified to make sure the ADC is not in the light path upon start up.

Thomas Augusteijn 2012-02-21