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| QC PLOTS |
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CURRENT |
HISTORY |
| Efficiency (vs.
time) |
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all plotted under CURRENT |
| Efficiency (vs.
wavelength) |
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all plotted under CURRENT |
| QC1 database (advanced users):
browse
| plot |
Click on CURRENT to see the current trending (Health Check).
Click on HISTORY to see the historical evolution of the trending. |
Since August 2006, a set of standard star measurements is taken regularly
with the Argus IFU of GIRAFFE, under CL (clear) or PH (photometric) conditions,
to measure the overall system efficiency. A set of three
settings is taken with the low-resolution grating (L427.2, L543.1, L881.7), three
more with the high-resolution grating (H447.1A, H651.5B, H875.7). These data are taken
approximately every 1 or 2 months.
They are calibrated with the robotic lamp flats. The flats
are used only for the localization solution (required for the extraction). Contrary
to the usual reduction, the extracted flat-field is not divided into the standard
star spectrum, in order to achieve the efficiency curve. The signal from all
fibres (excluding SKY and SIMCAL) is summed up and divided by the flux curve of the
standard star, to measure the overall (telescope plus optical components plus detector)
efficiency of the instrument.
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Argus STD frame.
This is the pipeline-recombined image of a GIRAFFE standard star measurement
taken with the Argus IFU. Each pixel corresponds to one fibre on the sky. The
bright spot at lower left is due to a bad column; the dark hole at upper right
is caused by the first fibres which are somewhat truncated by the CCD. |
QC1 parameters
| parameter |
QC1 database: table, name |
procedure |
| mean efficiency at central grating wavelength |
giraffe_std..mean_effic |
find central wavelength, average efficiency values in window of
2 nm size around that wavelength |
| qc_numsat |
giraffe_std..qc_numsat |
number of saturaed pixels in raw frame, to discover saturation |
| mean signal in recombined image |
giraffe_std..mean_signal |
replace pixel (4,4) by average from neighbours (to protect against bad column);
take average, to find cases with no STD star signal |
Trending
The mean efficiency is plotted in boxes 1-6 of the SYSTEM_EFFICIENCY trending
plot for 3 HR settings and 3 LR settings.
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Efficiency plots. Boxes 1-6 show
the mean efficiency displayed over time. The green bars mark the current ETC predictions. While there is good agreement of measured and predicted efficiencies
for the blue and middle settings, the ETC under-estimates the red efficiency
by a factor larger than 2.
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These data are also plotted over wavelength, in the SYSTEM_EFFICIENCY_WLN trending plot .
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Efficiency plot vs. wavelength. Box
1 shows the mean efficiency for the HR settings displayed over wavelength,
box 2 the same for LR. The green curve marks the ETC predictions.
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History
The trending plot covers the full history of this parameter.
| date |
event |
| 2006-08-06 |
first set of 6 efficiency monitoring frames taken |
| 2008-03-14 |
Old CCD ("Bruce") decommissioned |
| 2008-05-26 |
New CCD ("Carreras") operational; significantly higher efficiency
in the red, lower efficiency in the blue |
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