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| QC PLOTS |
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CURRENT |
HISTORY |
| Daily Health Checks: |
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| CD ALIGN DHC |
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| QC1 uves_zflat database (advanced users):
browse
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plot
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Click on CURRENT to see the last trending (Health Check).
Click on HISTORY to see the historical evolution of the trending. |
This tutorial provides information for the
Cross Dispersers
Health Check trending.
The Cross Dispersers trending is based on the measurement
of QC1 parameters of Cross Disperser [CD] Alignment technical
calibration data obtained with dedicated Health Check OBs executed
daily. These OBs obtain four sets of CD-Alignment data, one set for
each of the four CDs, each set comprising 2 RAW frames. The 2 RAW
frames of each set image the zeroth echelle order, with the CD being
moved away and then back into position between the two exposures. The
objective of the data is to measure the accuracy and precision of the
positioning of the CDs, in order to confirm that the CDs can be
repositioned in the morning after SCIENCE are acquired for acquisition
of calibrations.
QC1 parameters
- average y difference of zero orders (QC1 database table uves_zflat, column ydiffavg, product keyword QC.YDIFFAVG)
Description: Average order position shift. We monitor the Cross Disperser
position reproducibility
- rms of y difference (QC1 database table uves_zflat, column ydiffrms, product keyword QC.YDIFFRMS)
Description: RMS order position shift. We monitor the Cross Disperser
position reproducibility
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Cross-Disperser Alignment FLATs (a.k.a. ZERO ORDER FLATs)
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Purpose
The zero order flats are used to test the alignment and stability of
the positions of the four UVES crossdispersers (CD). They are measured
daily whenever UVES is operational and are a supplement to the format
check frames.
The zero order flats are measured within a sequence. There are two exposures
for each CD: the CD is moved from two opposite sides to the nominal position.
Differences in Y (cross dispersion) position of the zero orders indicate
problems in the positioning of the CD.
Modes
Each arm of UVES has two crossdispersers:
| CD |
INS MODE |
| 1 |
BLUE |
| 2 |
BLUE |
| 3 |
RED |
| 4 |
RED |
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QC1 parameters
The Y position of the zero order is measured at several X positions.
The average difference of the Y positions for each pair of zero flats
is calculated:
- average difference of Y positions (YDIFFAVG),
- rms of average Y difference (YDIFFRMS).
The trending plot shows YDIFFAVG versus
time. Values less than a few tenth of a pixel indicate good positioning
accuracy of the CDs.
Example for crossdisperser failure
An example for a failure of the red crossdispersers can be found in the
JAN-MAR 2004 plot. Note that the positioning
problems for CD#4 are indicated somewhat earlier than in the format
check plot.
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