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6.4.2 Calibration preparation

This step is in charge of preparing the spectra for the Calibration workflow: to select the calibrators, and to clean their spectra.

The wavelength calibration module needs high S/N spectra presenting deep absorption lines. Therefore the calibrators are selected based on their magnitude (external GRVS <9 mag) and on their atmospheric parameters (4500< Teff <6500 K). Figure 6.4 shows an example of a wavelength calibration star spectrum.

Figure 6.4: The RVS spectrum of a bright star used in wavelength calibration. The spectrum is dominated by the three Ca II lines. Some of the iron, and silicon absorption lines are also indicated. Figure from Sartoretti et al. (2018), by Olivier Marchal.