For each of the five observing modes required by the science case there is a specific set of fibre buttons within the positioner (two sets for the MO-LR and MO-MR modes to allow configuration of the next field to take place in parallel with the current observation). Each set of buttons is routed to a pair of fibre slits (one for each spectrograph). At the start of each observation the focal plate containing the configured fibre buttons is moved into the observing position, and the corresponding slits are moved into the active position in each of the two spectrographs. The gratings required for the observation are then selected in each of the four arms and the field is acquired using the fiducial fibres that have been deployed as part of the fibre-field configuration. The full set of possible observing modes envisaged for the instrument are illustrated in Figure 4 of RD5. Once the observing focal plate has moved into position, the robots will begin to reconfigure the opposing plate ready for its next target field. Each field that is to be observed on a given night will be fully configured during the day, so that daytime flat-field calibrations can be recorded in advance of the observations.
The OPTical Multi Object Spectrograph 'Extreme Visual Explorer' for the European - Extremely Large Telescope - Consortium partners: GEPI, NOVA, RAL, NBI, INAF, AIP, LSW, IAG, LNA, ON
