GMOS performance monitoring
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GMOS
- Measurement of throughput in imaging mode: observations required are imaging of photometric standards in (u)griz filters. Photometric weather is required, but observations can be performed during twilight. Observations for each filter are collected once a month.
- Measurement of throughput in spectroscopic mode: observations consist of spectroscopy of spectrophotometric standards with two gratings, one with peak response in the red (R150) and one in the blue (B600). Observations are taken using a 5'' slit at low airmass, to minimize the effects of differential refraction. The IFU mode as well as other gratings in long-slit mode can be calibrated through measurements of relative counts from flat-field exposures. Photometric weather required, but observations can be performed in twilight. Frequency is once every three months.
- Image Quality: Observations consist of images taken with guiding on, in good seeing conditions, at a range of elevations, with all filters. Exposure times have to be at least 30 seconds, in order to average out stochastic seeing variations. No dedicated observations are required for image quality monitoring---image quality is measured on images taken during normal science operations.
- Image fringing: Observations consist of seven dithered images obtained at relatively low airmass towards a blank field, in both i and z bands. Observations need to be guided, in order to make star removal easier. The OIWFS probe arm must not vignette the FOV in any dither position. Observations are collected once every six months.
- Detector cosmetics: Characterization and monitoring of detector artifacts, such as hot pixels and bad columns. Observations consist of dark exposures collected once a year.
