Quality Control: gain

VIRCAM Quality Control:
Gain

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gain | read noise | lamp


QC PLOTS
	CURRENT	HISTORY
gain [ e-/ADU ]
read noise [ e- ]
counts [ ADU ]
lamp flux [ ADU/sec ]
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Click on CURRENT to see the current trending (Health Check). Click on HISTORY to see the historical evolution of the trending.

The gain template generates two dome flats and two dark frames with the same exposure time. The statistical noise derived from the dark frames is called read out noise. The statistical noise derived from the flat frames and corrected for the read out noise is called photon noise, from which the gain is derived. The accuracy of these measurements are limited by the horizontal stripe pattern.

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QC1 parameters

parameter	QC1 database: table, name	procedure
gain	vircam_gain, qc_gain	- The gain is a conversion factor between the acquired electrons (e-) and the measured counts (ADU). The unit is e-/ADU. Two dome flats of the same flux level are subtracted from each other to minimize the structural noise. From the remaining random noise and the read noise derived from the dark frames the gain is obtained.

The gain is derived from a pair of equally exposed flat frames and a pair of dark frames acquired with the same DIT. The calibration frames suffer from a non-reproducible stripe pattern. Being not corrected for, the derived noise is biased and the resulting gain values can be up to 20% higher. For a detailed description, see the section on the horizontal stripes in the problems page.

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QC1 parameters

parameter	QC1 database: table, name	procedure
read noise	vircam_gain, qc_readnoise	- The read noise is derived from two consecutive dark frames. It is given in electrons (e-).

The read noise is derived from the pair of dark frames. Since the non-reproducible stripe pattern is not corrected for, the value of QC parameter is composed by the detector read and the variability of the stripe pattern in consecutive frames. For a detailed description, see the section on the horizontal stripes in the problems page.

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QC1 parameters

parameter	QC1 database: table, name	procedure
counts	vircam_gain, qc_counts	- The counts acquired in the flat frame in ADU .
lamp flux	vircam_gain, qc_flux	- The counts acquired in the flat frame divided by ( DIT * NDIT), given in ADU/sec. The VIRCAM detector controller is configured that NDIT >1 does accumulate (sums up) counts on the chip, while for other VLT instruments NDIT >1 means averaging on the chip. Therefore we divide here by DIT and NDIT.