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Gaia Data Release 2
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Table 1

CCD performance in terms of the video-chain total detection noise as measured from the second of the two prescan samples available for each CCD, but summarised via a mean and standard deviation over all CCDs grouped by instrument.

Instrument Mean gain Total detection noise per sample
and mode ADU/e Required/e Measured/e Measured/ADU
SM 0.2569 13.0 10.829 ± 0.494 2.782 ± 0.127
AF1 0.2583 10.0 8.556 ± 0.438 2.210 ± 0.113
AF2–9 0.2578 6.5 4.326 ± 0.648 1.115 ± 0.167
BP 0.2464 6.5 5.170 ± 0.362 1.274 ± 0.089
RP 0.2484 6.5 4.752 ± 0.175 1.180 ± 0.043
RVS-HR 1.7700 6.0 3.272 ± 0.155 5.791 ± 0.274
RVS-LR 1.8185 4.0 2.907 ± 0.177 5.286 ± 0.322

Notes. The analysis period used was July 2014 to November 2016 and covers the entire science operational period of DR2. Measurements are given in analogue-to-digital units (ADU) and electrons using the gain measurements quoted in the second column, where the gain was measured on-ground prior to launch (this cannot be measured in-orbit owing to the non-availability of flat field illumination). All instruments are statistically well within the design requirement quoted in the third column. For the RVS instrument, the measurements are subdivided into high-resolution (HR) and low-resolution (LR) modes where the latter samples are hardware binned on-chip by 3 pixels in the along-scan direction. This observing mode was used only briefly at the start of the mission (Cropper et al. 2018). Note the larger gain in the RVS: this is the main contributor to the greater impact of the bias non-uniformity in this instrument.

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