Internal Flatfield Lamp WarmUp Time

It has been known since the days of FEROS at the ESO-1.52m that the Flatfield Lamps require some time to warmup before their output flux stablises, however it has apparently never been systematically investigated how long is actually required to reach the stable operation regime. This report gives a quick answer to this perenial question.

Data acquisition and reduction

On the night of 2005-10-03/04, which was otherwise lost to poor weather conditions, several hours after a standard DRS initialisation (to allow the FF lamps to fully cool back to room temperature), a sequence of 30 FFs were acquired in the fast readout mode. These data were reduced using the FEROS-DRS package available from here using the write/key RedAllIms/c/1/1 "Y" option to force the DRS to process the flatfield images.

Results

The plots below clearly show that the FF flux has stabilised approximately 6mins after the OB is started. Therefore the currently adopted 5min warmup used in the StanCal OBs and in CalOB is probably just adequate and reasonable since there is generally of the order of 1 additional minute of overhead due to moving functions etc.

Warning

Presumably the required warmup time can vary according to the state of the lamp, after many hours of use the required warmup may increase, therefore this test should be repeated from time to time.