QC PLOTS
STD Zeropoints:	CURRENT	HISTORY
zeropoint u_SDSS
zeropoint g_SDSS
zeropoint r_SDSS
zeropoint i_SDSS
zeropoint z_SDSS
zeropoint B_JOHN
zeropoint V_JOHN
master twilight flat level
STD Image Quality:
fwhm u_SDSS
fwhm g_SDSS
fwhm r_SDSS
fwhm i_SDSS
fwhm z_SDSS
ellipticity u_SDSS
ellipticity g_SDSS
ellipticity r_SDSS
ellipticity i_SDSS
ellipticity z_SDSS
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.

During normal VST/OmegaCAM operations standard star frames (DPR.TYPE = STD,ZEROPOINT) are taken on the same night matching each filter for which science data was obtained. The data consists of a single standard star field of similar airmass and identical filter. To monitor the ambient conditions (extinction) another standard star observation is made of the polar field (DPR.TYPE = STD,EXTINCTION) at the beginning, middle, and end of the night.

The standard frame is bias corrected, flat-fielded, background subtracted, and trimmed. SExtractor is run on the image and is cross-matched to sources present in the external standard star catalogue (REFERENCE_STAR_CATALOG). The apparent magnitudes of the SExtractor catalogue and the absolute magnitudes of the REFERENCE_STAR_CATALOG is used to define the zeropoints for each detector. The zeropoints monitored for the health check plots are derived from flux units of electrons/second.

The pipeline creates four output frames from its standard star recipe (omega_standard_star): a reduced standard star image (OC_PSTD_<date>_1_1_normal_normal_<filter>.fits), a photometric fits table listing each secondary standard star source detected in each detector (OC_PPHO_<date>_1_1_normal_normal_<filter>.fits), a fits table listing the computed zeropoints for each detector (OC_PZPT_<date>_1_1_normal_normal_<filter>.fits), and a mask of bad pixels, saturated pixels, and satellite trails for the reduced standard star image (OC_PSMA_<date>_1_1_normal_normal_<filter>.fits).

The full OmegaCAM reduced standard frame (r_SDSS filter).

A single detector (ESO_CCD_#71) OmegaCAM reduced standard frame (r_SDSS filter).

A single detector (ESO_CCD_#71) OmegaCAM reduced standard mask (r_SDSS filter). A value of 1 indicates a bad pixel; otherwise 0.

QC1 Health Check Plots

The QC1 health check plots for the OmegaCAM standard stars consist of monitoring the zeropoints for each of the following filter sets: u_SDSS, g_SDSS, r_SDSS, i_SDSS, z_SDSS, B_JOHN, and V_JOHN. In each case, the average zeropoint, its rms, and the zeropoints of the individual detectors are monitored.
Furthermore, the standard stars contribute to a monitoring of the image quality via a measure of the image FWHM vs. the corrected (corrected for waveband and airmass) DIMM seeing values and the ellipticity values measured for stellar sources. These are plotted for the standard Sloan bands (u_SDSS, g_SDSS, r_SDSS, i_SDSS, and z_SDSS).


Zeropoints:

• for each of the filters: u_SDSS, g_SDSS, r_SDSS, i_SDSS, z_SDSS, B_JOHN, and V_JOHN:
  • zeropoint as averaged over all 32 detectors
  • zeropoint rms averaged over all 32 detectors
  • zeropoints for each individual detector
  • score outliers
    

Image Quality:

• for each of the filters: u_SDSS, g_SDSS, r_SDSS, i_SDSS, and z_SDSS:
  • image quality plotting the stellar source FWHM vs. the corrected (for airmass and waveband) DIMM seeing (arcsec)
  • the difference in the standard star FWHM vs. the corrected DIMM seeing (arcsec)
  • score outliers
• for each of the filters: u_SDSS, g_SDSS, r_SDSS, i_SDSS, and z_SDSS:
• the stellar source ellipticity (1 - b/a) averaged over all 32 detectors
• the stellar source ellipticity rms averaged over all 32 detectors
  
• the stellar source ellipticity for each individual detector
• score outliers

QC1 parameters (trended for each individual detector)

QC Reports for the standard star frames

QC Report 1:
left: full-field image of the reduced standard star field of the extension listed at the top of the image
center: full-field image of the reduced standard star field with detected USNO-A2 stars marked with blue circles. If the USNO-A2 star has an ellipticity >= 0.20 the marking circle is black.
right: a 4x zoom of the center area of the reduced standard star field. At the far right of these images, a number of data parameters are listed.

QC Report 2:
top left: A histogram of the FWHM measured for all detected sources having CLASS_STAR <= 0.90 and mag_auto <= 19.0.
A Gaussian fit to the FWHM histogram is shown (dotted red line) and its values indicated in the legend. The QC header STD.SEEING is shown as a vertical green line and the corrected DIMM seeing (corrected to the wavelength of the STD observation and the airmass) is shown as a vertical red line.
top right: A histogram of the ellipticity (1 - B/A) measured for all detected sources having CLASS_STAR <= 0.90 and mag_auto <= 19.0.
A Gaussian fit to the ellipticity histogram is shown (dotted red line) and its values indicated in the legend. The QC header STD.ELLIPTICITY is shown as a vertical green line and the critical ellipticity limit of 0.20 is marked as a red vertical line.
bottom: The background level (in ADU) measured around each detected source as a function of its radial position from the bottom left-hand corner of the image. A least-square fit to the radial dependence of the background and the background median is given in the legend.

QC Report 3:
top: The ellipticity (1 - B/A) of each detected source as a function of its radial position from the bottom left-hand corner of the image. The median ellipticity is shown as a green line and is given in the legend. The critical ellipticity limit of 0.20 is marked as a red dotted line.
bottom: for ALL detectors the zeropoints are plotted for both the current standard star field (blue points) and the reference standard field (red points). The zeropoint of the current detector viewed in the other QC reports is marked with a circle. The median zeropoint of all detectors is shown as a blue (current) and red (reference) dotted line and is listed in the legend. The shaded green area is the +/- 1sigma scatter of the current zeropoints.

Trending and Issues

The input standard star reference catalogue for the equatorial and polar fields (REFERENCE_STAR_CATALOG => OC_GSTD_111125_ALL.fits) is not yet complete. As a result, some star fields will lie outside of the standard star coverage and will not be able to provide zeropoints. This is particularly true of the polar field which is currently not included in the catalogue. This will improve as the VST/OmegaCAM coverage matures.

History