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VISIR Quality Control:
Imaging Standard Star frames

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Trending & QC1
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Data Management
QC links:
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sensitivity | conv. factor | background
conv. factor
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.

A number of VISIR imaging standard star observations is taken every night. They are acquired using different filters (INS.FILT1.NAME) and pixel-field-of-view (INS.PFOV). They are important not only as photometric flux calibrators, the imaging standard stars are also used for tracking changes of the MIR observing conditions throughout the night. The VISIR calibration plan requires the imaging standard stars to be taken within 3 hrs (+/- 3 hrs) from the science imaging frames.

Imaging Standard Star frame . This is an example of the imaging standard star frame which is a pipeline product of the "visir_img_phot" recipe. Note persistent horizontal stripes characteristic for the detector.

top sensitivity

The following plot shows the temporal evolution of the sensitivity determined from the imaging standard stars observed in filter PAH1 and pixel-field-of-view 0.075 (panel 1) and 0.127 (panel 2). This instrument setup was selectec as the most frequently used.

However, we also monitor sensitivities in different filters. The N-band plot shows sensitivities recorded in the N-band filters: PAH1 (8,6 um), SIV (10.5 um), PAH2 (11.25 um), NEII (12.8 um), while the the Q-band plot thise observed in the Q-band filters: Q1 (17.65 um), Q2 (18.7 um), Q3 (19.5 um).

QC1 parameters

  • sensitivity (QC1 database table visir_zp_img, column sensit)
    Sensitivity is determined by observing standard star and extrapolating to estimate the limiting flux expected in 1 hour "on-source" integration of a point-source detected with S/N of 10. It's given in units: mJy at 10 sigma in 1 hr.
top conv. factor

QC1 parameters

  • conv. factor (QC1 database table visir_zp_img, column conver)
    The conversion factor describes conversion between ADU and Jy. It is computed as: F(tot.observed) / F(model) [ADU/Jy], where F corresponds to flux and F(model) is the model predicted flux of the standard star from a catalog.
top background

The following plot shows the background level as a function of time.

QC1 parameters

  • background (QC1 database table visir_zp_img, column backgd_mean)
    The mean background level is measured from the Half-cycle frames. Its value can vary between -32000 and +32000 ADU.