There are three kinds of quality control (QC) plots:
- the overview plot, displaying the fluxes (rebinned to 5A) and S/N slopes for all settings (wavelength ranges)
- the quality plots for each setting, with the fluxes as 5A rebin and a more detailed S/N plot
- an overview of all individual input spectra per setting, again as 5A rebin.
1. Overview plot.

This plot has two parts. The upper parts shows the final, co-added spectra in all 6 spectral ranges plotted together: in red, data taken in dichroic#1 mode (346 and 580L/580U settings); in black, dichroic#2 mode (437 and 860L/860U). They are binned here to 5 Angstroem resolution.
In general, fudge factors have been applied to force the red spectra to match the black spectra. In green, we display the
corresponding HST-STIS spectrum (if available). It has been downloaded from http://archive.stsci.edu/prepds/stisngsl/datalist.html.
The second plot displays the signal-to-noise ratio of the co-added spectra. The S/N has been derived by dividing the final, co-added spectra (top) by the corresponding sigma file, multiplied with square root of N (the number of input files as listed in the overview table).
There is one overview plot per target.
2. Quality plot.

This plot has again two parts and is a more detailed version of the overview plot. It comes per spectral setup. There is again on top the
co-added spectrum, binned to 5 Angstroem. The second plot has, in blue, the S/N ratio (same as in the overview plot), plus
a more direct measurement of the S/N ratio based on the rms fluctuations in 0.5 Angstroem bins. These numbers are displayed as red dots.
In many cases stellar absorption lines or telluric lines dominate the fluctuations and corrupt the S/N value.
But in favourable cases a spectral region may show pure continuum and give a realistic estimate of S/N.
Hence the upper envelope of the red dots can be seen as a S/N measurement of the final product spectrum,
including all noise sources up to a scale of 0.5A.
There is one overview plot per target and setup, in total six per target. They are linked on the target overview page under the link "Quality plots".
3. Plot with input spectra.

This plot displays all input spectra and their average (file extension _avg.fits). All displayed spectra are rebinned
to 5 Angstroem resolution. This plot visualizes the flux scatter of the input spectra (due to slit losses induced
by variable seeing, or variations in transparency or other ambient conditions). As a filler programme, these data were taken under variable conditions. This quality control plot has been used to identify, and sometimes even reject, input spectra with very low flux, or with a distorted slope.
There is one such plot per target and setup, in total six per target. They are linked in the target overview table under the column "N" (number of exposures).
Send comments to <Reinhard.Hanuschik@eso.org>
Last update: 2009-10-05 17:52:42