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UVES Quality Control:
Bias

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QC PLOTS
  CURRENT HISTORY
median level (master)
read-out noise (master)
read-out noise (raw)
structure in X (raw)
structure in Y (raw)
QC1 uves_bias 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 BIAS Health Check trending. It is based on the measurement of QC1 parameters of BIAS calibration data obtained with dedicated Health Check OBs executed daily. These OBs obtain four sets of BIAS data, 2 sets in BLUE mode and 2 sets in RED mode, each set comprising 5 RAW frames. The 2 sets in each mode are acquired in the two main CCD ReadOut modes:; 225kHz, low gain, 1x1 and 50kHz, high gain, 2x2.

These data thus give detailed charateristics for all THREE UVES CCDs, one BLUE and two RED (UPPER and LOWER). Trending is provided for:

top Bias parameters

QC1 parameters

  • median value of master bias (QC1 database table uves_bias, column median_master, product keyword PRO.DATAMED)
    Exact median of the pixel values in the frame. All pixels are taken into account.
  • RON value of master bias (QC1 database table uves_bias, column sigma_master, product keyword QC.OUTi.RON.MASTER)
    Read noise in ADU
  • RON value of first raw frame (QC1 database table uves_bias, column sigma_raw, product keyword QC.OUTi.RON.RAW)
    Read noise in ADU
  • structure in X direction (QC1 database table uves_bias, column struct_row, product keyword QC.OUTi.STRUCTX)
    Evidence of any possible structure in bias. To have more details on a bias image without saving the full image we collapse it along X or Y and compute the standard deviation of the corresponding point distribution. This is the STRUCTX/Y. A large or suddenly changed value of the structure indicates some problem on the axis orthogonal to the direction of collapse.
  • structure in Y direction (QC1 database table uves_bias, column struct_col, product keyword QC.OUTi.STRUCTY)
    Evidence of any possible structure in bias. To have more details on a bias image without saving the full image we collapse it along X or Y and compute the standard deviation of the corresponding point distribution. This is the STRUCTX/Y. A large or suddenly changed value of the structure indicates some problem on the axis orthogonal to the direction of collapse.
top Structure

Remnants in red 2x2 BIAS frames

From time to time, there appear outliers in the HC plot "Struct_Y", #6 ("REDU 2x2 high"). These are due to remnants left by previous arc observations. Arcs taken in 760-860nm settings are known to leave this kind of remnances. (For this reason the scripts preparing the morning calibrations is asked to take the arcs at the end of the sequence, but occasionally this does not work.) Usually such master_bias frames should be rejected, only good ones should be associated to science frames.


Outliers in the HC plot "Struct_Y", #6


Left: remnants from overexposed arc lines; right: a clean BIAS without remnants. The collapsing in Y preserves somehow the additional signal and therefore causes a red score.

top History

A FULL history trending plot of the BIAS median levels is available here.
Other significant events during the instrument's lifetime:

2009-06: The RED UPPER CCD was exchanged.


 
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