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Quality Control and
Data Processing
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KMOS: Lamp flat fields
Flat-field exposures are measured during daytime for the five wavelength bands IZ, YJ, H, HK, and K and for six different rotator angles. A standard calibration sequence uses rotator angles of -60 (i.e. 300), 0, 60, 120, 180, and 240 degrees. Each IFU comprises 14 slices. Eight IFUs form a sub group which is mapped on a single slit. The light is then dispersed through one of the three spectrographs and recorded on one detector array (out of three). There are three independent optical channels, each having eight IFUs.
Flat-field slitlets
The average width of each slitlet and their position on the detector is monitored for each spectral band. The QC parameters at 0 degree rotator angle (slit_wid_mean_0, slit_edge_x_0) are plotted versus time and scored. The dependency from rotator angle is shown in separate plots (not scored). The number of bad pixels is trended for all bands in a single plot. The parameter badpix_0 is plotted versus time. Since the number of bad pixels is dominated by the pixels between the slitlets, this parameter is chiefly useful to detect IFUs that are not operational. Any missing IFU increases the number of bad pixels by about 400000. The trending of bad pixels is complemented by the number of active IFUs. These are the IFUs that could be identified and processed during pipeline-processing of flat fields. Data from all spectroscopic bands are combined in one plot. The QC1 parameter for 0 degree rotator angle is trended versus time and scored. The dependency from rotator angle is shown in a separate plot (not scored). Scoring&thresholds Flat-field slitlets Changes in the slitlet positions should not be larger than +/- 1.5 pixels in normal operations. After a warm-up of the instrument, jumps in the positions can occur and adjustments of the thresholds are typically necessary. The nominal width of the slitlets is 14 pixels. In practice, it is a bit lower, typically around 13.5 pixels with some variation from detector to detector and between the five wavelength bands. There is a dependency on the focus of the respective sprectrograph and changes have been observed sometimes after interventions. Scoring thresholds for the slitlet width have been set empirically to +/- 3 sigma around the median (determined from data taken between 15 August and 30 November 2018). When all IFUs are operational, upper and lower thresholds for the IFU number are identically set to 8. If an IFU is put out of operations then the lower threshold must be updated accordingly. The number of bad pixels is not scored. There have been several periods when KMOS was not operated with the full number of IFUs, especially from 2013 until early-2015.
slit_edge_x_<n>: Average x position of left edge of leftmost slitlet on each detector, for rotator angle 0. with <n> = 0, 1, ..., 6. <n> = 0 denotes the value for a rotator angle of 0; <n> = 1, ..., 6 denote the values for the first, second, etc. rotator angle position in the calibration sequence. These typically refer to rotator angle values of -60, 0, 60, 120, 180, and 240 degrees.
Flat-field lamp performance
KMOS flats are usually taken at six different rotator angles. These fill the QC parameters flat_eff_1, flat_eff_2, ..., flat_eff_6. The actual angles can be found in the parameters rot_angle_1, rot_angle_2, ..., rot_angle_6. The parameter flat_eff_0 is only filled if a measurement at 0 degree rotator angle is present (which is usually the case for daytime calibrations).
The performance of the tungsten flat-field lamp is monitored for all three channels in the YJ band. Three plots show flat_eff_0 versus time. Since the flat efficiency does not strongly depend on rotator angle, only flat_eff_0 is scored. Three other plots show flat_eff_1, ..., flat_eff_6 versus rotator angle. Scoring&thresholds Flat-field lamp performance Thresholds have been set empirically. Adjustments of the scoring thresholds have been necessary a few times after interventions. Algorithm Flat-field lamp performance Pipeline calculated average flat-field flux, converted to e-/sec.
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