Correction of airmass

The correction of airmass is presented in appendix A . We still used here the terms of airmass ( $X$ is written with the first order as follows:

$$zero = zero_{airmass = 0 } + K_\Lambda X$$ (8.19)

Items zeros and the term of airmass ELIXIR are expressed for a airmass of 1, zero point is written then:

$$zero = zero_{airmass = 1 } + K_\Lambda (X-1)$$ (8.20)

After this last correction, we have zero points of our images of primary calibration. They is necessary for us now to propagate these zero points towards the images which are used as photometric reference for the lightcurves: coadditionnées images of better seeing.