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gaia early data release 3 documentation

6.2 Properties of the input data

6.2.2 Initial calibration models

The input data of the spectroscopic pipeline include some initial calibration data obtained off-line.

The first guess calibration models are provided in the form of trending functions for each calibration parameter (Section 6.3). The input data model contains the initial coefficients, the trending functions for each calibration coefficient and the start and end time of the trending epoch. There is one record for each calibration type (Wavelength, GrvsZeropoint, LSF-AL, LSC-AC, Photometric), and each configuration (FoV, CCD) and trending epoch. The initial coefficients for the wavelength calibration are computed after off-line analysis of the data, and using the on-ground measurements for the LSF-AL model.

The calibration model for the wavelength calibration, and for the GRVS zeropoint are updated in the Calibration workflow in Figure 6.2 and used in the downstream workflows. For the other calibrations, like the LSF, that are not running in the pipeline, the initial model is not updated and the nominal on-ground values are used.

A table containing the coefficients of the bias non-uniformity calibration is also input. The coefficients are obtained during the daily processing and are needed by the bias non-uniformity mitigation module, integrated in both the CalibrationPreparation and FullExtraction workflows (Figure 6.2).

A table, containing the CCD information, like the bad column positions, the gain, the saturation level, obtained using on-ground information, is also input.

Given that this version of the pipeline does not include the straylight level calibration, the initial straylight flux map, obtained using only the Trending Epoch-0 data (Figure 6.1 and Section 6.3) is input, and used for the correction of the straylight background in the spectra of all trending epochs.