On the importance of Earth's atmosphere for SNIa precision cosmology

Abstract: The measurement of colours in photometric surveys is a path to get access to cosmological distances. But for future large surveys like the Large Survey of Space and Time undertaken by the Vera Rubin Observatory in Chile, the large statistical power of the promised catalogues will make the photometric calibration uncertainties dominant in the error budget and will limit our ability to use it for precision cosmology. The knowledge of the in situ atmospheric transmission for each exposure, each season and on average for the entire survey can help reaching the subpercent precision for magnitudes. I will show the impact of precipitable water vapour during a cosmological survey on supernova cosmology. Then I will present how AuxTel at the Vera Rubin Observatory have the capability to measure the on-site atmospheric transmission in real time to improve LSST photometric calibration for precision cosmology.