QC PLOTS
	CURRENT	HISTORY
Daily Health Checks:
ECH FMTCHK GratPos BLUE 346
BLUE 437
REDU 580
REDU 860
REDL 580
REDL 860
Thermal coefficients:
ECH FMTCHK Thermal BLUE DHC
REDU
REDL
QC1 uves_fmtchk 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.

This tutorial provides information for the Echelle grating position. It is based on the measurement of QC1 parameters of FORMAT CHECK calibration data. These are obtained with dedicated Health Check OBs executed daily. These OBs obtain four sets of FORMAT CHECK data, 2 sets in BLUE mode and 2 sets in RED mode, each set comprising a single RAW frame. Each set is acquired in a different wavelength setting covering the two arms and the four cross dispersers.

QC1 parameters

The recipe performs a comparison between the detected line positions and the physical model. This is useful to verify the precision of physical model prediction and instrument spectral format stability.

• average temperature of camera [C] (QC1 database table uves_fmtchk, column ins_temp1_mean, product keyword INS.TEMPi.MEAN)
  Description: Mean Temperature during the exposure.
• difference of X positions to physical model (QC1 database table uves_fmtchk, column mean_dx, product keyword QC.MODEL.DIFFXAVG)
  
• difference of Y positions to physical model (QC1 database table uves_fmtchk, column mean_dy, product keyword QC.MODEL.DIFFYAVG)
  
• number of lines selected (QC1 database table uves_fmtchk, column nlin_sel, product keyword QC.MODEL.NLINSEL)
  

QC1 parameters

The recipe also performs a comparison between the detected line positions and a reference frame. This information is in principal redundant but monitored to safeguard against instabilities in the physical model prediction.

• median of difference in X to reference frame (QC1 database table uves_fmtchk, column median_shftx, product keyword QC.SHFTXMED)
  
• median of difference in Y to reference frame (QC1 database table uves_fmtchk, column median_shfty, product keyword QC.SHFTYMED)
  

These parameters are stored in the QC1 database but not monitored on the HC monitor to avoid redundancy of alerts.

Modes

Formatcheck frames are measured daily whenever UVES is operational. They are used to monitor the orientation of the four crossdispersers and the two gratings. For each crossdisperser, one standard setting is used:

grating setting 1 DI1 346bl_1x1 2 DI2 437bl_1x1 3 DI1 580re_1x1 4 DI2 860re_1x1

QC1 parameters

Five QC1 parameters are measured:

• the shifts in X and Y of the spectral format in the monitor frame against the physical model (mean_dx, mean_dy), the shift (cross-correlation) of the monitor frame against a fixed reference frame (median_shftx, median_shfty)
• the number of lines selected by the pipeline recipe (nlin_sel).

The results of the comparison to the physical model are plotted. The shifts are evaluated as function of time and as function of temperature T which is the main parameter for daily drifts. Typically 300-1100 lines are selected per CCD for this analysis.

These QC1 parameters are plotted for all four settings. The red settings have data for the two CCDs (REDU and REDL).

Y drifts versus temperature

A compensation for thermal drifts in X and Y is active since November 2000 for all four gratings. Their coefficients are monitored in the HC plots "Thermal_<ccd>".

Notes (until 2003)

1. A 5.9 mag earthquake on 2000-05-12 shifted the blue gratings by more than -10 pixels (see DY panels 346B, 437B from Apr-Jun2000). The blue gratings have been readjusted on 2000-07-24.

2. In addition to thermal Y drifts, there are from time to time sudden shifts (e.g. earthquake, readjustments). Also slow non-thermal Y drifts (timescale of months) have been observed.

3. Since 2001-12-26, a thermal compensation in X (dispersion) direction has been activated.

4. The trending of N_sel gives an indication about the quality of the DY correlation. If the Y position of a grating starts drifting away from its nominal zeropoint (or is suddenly pushed away), then usually N_sel is the most sensitive parameter for detecting whether or not this is critical and requires immediate reaction. A good example is the period JUL-SEP 2001 where the N_sel parameter for grating 4, REDU CCD, faded away from its reference value (about 320) to less than 200. This indicated a critical regime at least for the UVES pipeline to find the proper dispersion solution.

5. From 2002-05-29 to 2002-06-17, the positons of the red crossdispersers could not be set with high accuracy. This was caused by high friction and contamination of the red crossdisperser bearing. The crossdispersers have been repaired on 2002-06-17. All observations which have been affected by this problem have been re-scheduled.

Events

A list of events which affect the grating positions is available (until 2003).

See also the history of the HC plots for a more complete data history.