ON-SKY CHARACTERIZATION ITEMS Note: in case of measurement of sky properties, the measurement listed is to be carried out in every appropriate filter. Repeatability of filter placement is probably a good thing to test also - this can be done in a number of the tests below I guess **** yes definitely **** DETECTOR NOISE PROPERTIES The detectors will be being used in a new mains power environment, attached to a telescope, and may have noise properties different to those measured in the lab. The difference needs to be characterized so that its impact on data reduction can be assessed. Also remeasure crosstalk matrix in the on-telescope state. Bad pixel stability should be assessed as soon as possible so we should be taking bias and dark frames from the very start. **** include re-assessing the repeatability and level of the reset anomaly/ dark stability **** SKY EMISSION Brightness, time variation, spatial scales of the emission. Effect of large spatial offset to a "sky" position. Sky brightness vs. distance from Moon (check for additional contribution from scattered light). Sky brightness as function of zenith distance. FRINGING Fringe amplitude and stability during change of sky brightness. Variation time and spatial scales, speeds of motion. SENSITIVITY Need an early measurement of the sensitivity limit in the standard observing modes. Also should compare coadded images of the same field taken on widely-separated nights. Quantify overheads in standard observing modes. BACKGROUND LIMIT Check early what exposure time is needed to reach background limit. COSMIC RAYS Long exposure to pick up a lot of CRs - test whether DR rejects them. PERSISTENCE Check in a field with a range of point-source brightnesses **** possibly repeat at further intervals to check on temporal stability of effect **** FLAT FIELD Dome flats, frames taken close to twilight - usable ? Nonlinearity measurements in here too (might be difficult to always do at the same time since STARE mode needed for nonlinearity measurements). Vignetting function and its motion if any. Tests of different flat fielding algorithms. **** need to assess stability of flats since impacts on data taking and reduction strategy **** **** nonlinearity measurements are done using dome flats so not quite sure what the above comments is referring to **** **** will we have a means taking of dome flats/linearity checks with stable illumination source and screen ? **** SCATTERED LIGHT Observe a field with large numbers of stars. See if we can measure the scattered light. **** may be easier to interpret with a few bright stars **** CALIBRATION DETAILS Place a UKIRT faint standard on each chip independently (possibly even in each of the different channels on each chip?). Visit a number of standard fields. ASTROMETRY Dead-reckoning coordinate system - first go. **** should be easy enough once we figure out which way up the detectors have been read out, also add refining the WCS constants and in particular the radial distortion model since needed later for more accurate astrometry **** **** could use this to check microstepping accuracy - is it n+1/2 pixel ? **** GUIDING Guiding in crowded fields needs to be tested. **** and in the middle of large extended objects **** STANDARDS **** we would like to include first epoch measurements of secondary standard fields as early as possible - not technically on-sky characterisation, but we would like to see a commitment to devote significant time to standards in these early WFCAM phases **** **** do we want to include a mesostep sequence early on ? ****