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UVES Quality Control:
Cross_Disperser_Alignment

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QUALITY CONTROL
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CD ALIGN : mean Y value
rms of Y value
QC1 uves_zflat database (advanced users): browse | plot
   Click on CURRENT to see the last trending (Health Check).
   Click on HISTORY to see the historical evolution of the trending.


top Introduction

This tutorial provides information for the cross dispersers Health Check trending. It is based on Cross Disperser [CD] alignment 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.  
top QC1 parameters

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

top Cross-Disperser Alignment FLATs (ZERO ORDER FLATs)

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

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).

 
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