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VIMOS Quality Control:
MOS standard star exposures

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Trending & QC1
   MOS effic
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MOS efficiency
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.

Spectrophotometric standard stars are observed for all grisms dependent on the usage of the settings for science. Their purpose is to monitor the overall instrument efficiency (telescope+instrument+detector) and to provide a measure of the spectral response. In MOS mode, standard stars are observed with dedicated masks having eight slits where the standard star is present in one of them.

Information about response curves and flux calibration can be found here. MOS observations of standards can suffer from slit losses. An example is provided here.

top Efficiency from spectro-photometric standard stars

The VIMOS pipeline extracts the signal of the standard star in the same way as for science observations. Then, the efficiency curve is calculated as the ratio of the observed flux (in e-/sec/A) at airmass one and the catalog flux of the star (converted to the expected number of electrons). The response is the ratio of the catalog flux to the observed flux (for airmass one). For the purpose of Quality Control, the efficiency is resampled at 15 fixed wavelengths from 3700A to 9300A with 400A step size.

QC1 parameters

parameter QC1 database: table, name description
MOS efficiency vimos_mos_std, efficiency1 efficiency (ratio of the detected number of photons to the real number of photons) at 3700A
vimos_mos_std, efficiency2 efficiency at 4100A
vimos_mos_std, efficiency3 efficiency at 4500A
vimos_mos_std, efficiency4 efficiency at 4900A
vimos_mos_std, efficiency5 efficiency at 5300A
vimos_mos_std, efficiency6 efficiency at 5700A
vimos_mos_std, efficiency7 efficiency at 6100A
vimos_mos_std, efficiency8 efficiency at 6500A
vimos_mos_std, efficiency9 efficiency at 6900A
vimos_mos_std, efficiency10 efficiency at 7300A
vimos_mos_std, efficiency11 efficiency at 7700A
vimos_mos_std, efficiency12 efficiency at 8100A
vimos_mos_std, efficiency13 efficiency at 8500A
vimos_mos_std, efficiency14 efficiency at 8900A
vimos_mos_std, efficiency15 efficiency at 9300A


For each grism, one QC1 efficiency parameter is monitored over time as a measure for the time dependency of the overall efficiency in each setting. The following associations are used:

grism name QC1 parameter name wavelength
LR_blue efficiency4 4900A
LR_red efficiency9 6900A
MR efficiency8 6500A
HR_blue efficiency6 5700A
HR_orange efficiency7 6100A
HR_red efficiency9 6900A

In addition to the trending over time, overview plots showing the spectral distribution of the efficiency for all wavelengths are also available.

before 2010 intervention
after 2010 intervention
with new HR_blue grism installed March 2012


date event
2010-07 new detectors with increased efficiency in the red
2012-03 new HR_blue grism