Modes

DARK frames (CATG = CALIB, TYPE = DARK, TECH = IMAGE) are measured occasionally, for the BLUE and RED arms separately, with the shutter closed. They are used to measure the dark current. They come in 1x1 and 2x2 binnings. They have typical exposure times of 1 hr.

There are also DARKs with short exposure times, typically 60 secs. These are used for CCD cleanup and are useless for monitoring the dark current.

There are also open-shutter DARKs (since December 2001: CATG = CALIB, TYPE = PARASITIC, TECH = IMAGE). They include, in addition to the CCD dark current, contribution from the camera enclosure. During commissioning, there has been found a level of luminiscence in the blue camera which, on data from March 2001, is still persistent. It amounts to roughly 11 ADU/hr/4px or about 1.7 e^-/hr/px. Hence this contribution dominates the effective dark current in the blue. It most likely originates from Cerenkov radiation due to radioactive decay.

QC1 parameters

Dark current. The UVES pipeline generates master DARKs from input raw DARKs. A master BIAS is subtracted. The mean of the residual pixels is calculated and transformed into the dark current.

Usually results from the 1x1 darks are unreliable since the dark current is actually very low. Hence all numbers given here are for the 2x2 bin mode. They are in units of [ADU/hr/4px]. The transformed values in electrons per hour have used the conversion factors 0.60 electrons per ADU for the blue, and 0.52 electrons per ADU for the red CCDs.

* mean for 2001
** refers to numbering in QC plot