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Michelle performance monitoring

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  • Emissivity: This provides an indirect assessment of mirror reflectivity. The procedure consists of taking two echelle spectra, one pointing at the zenith, the other taken with the mirror cover closed. The ratio between the two spectra in a telluric line-free spectral region, provides the mirror emissivity. These data require dry conditions, and can be collected in twilight, once every six months.


  • Center of rotation: The positions of the field rotation center and the slit rotation center have been seen to be no longer coincident. This needs to be corrected and henceforth monitored. The field rotation center is determined from observations of a star with the grating in zero order at varying field rotator positions. The slit center is determined on the basis of daytime slit images taken at 0 and 90-degree orientations. Observations require dry conditions, but can be executed in twilight. Frequency needed is once every other year.


  • Spectroscopic hot spots: The position of the spectroscopic hot spot has been seen to vary. This is a crucial piece of information for optimal spectroscopic observations. The positions of the hot spots for different observing modes need to be determined and monitored. This is performed by performing peak-up with the slit rotated at 0 and 90 degrees. Attention for the fact that spectroscopic hot spots for the lowN and lowQ modes require very dry conditions. Observations will be collected every six months.


  • Imaging throughput and image quality: Observation required is imaging of standard stars. Data can be collected in twilight, but require photometric and dry conditions. Frequency required is once a month, whenever the instrument is on the telescope.


  • Spectroscopic throughput: Observation required is spectroscopy of standard stars. It can be executed in twilight, but requires photometric, dry conditions. Frequency will be once every six months.