Dealing with systematic errors in LSST: observational systematics and color corrections

With the arrival of large galaxy surveys such DES, DESI and Euclid and their ability to observe millions of galaxies, cosmology has become a precision science. In the coming years, the Large Survey of Space and Time (LSST) will start to carry out a massive survey which will provide data with such low statistical errors that systematic effects will become the main source of uncertainty. Therefore, dealing with them will be one of the main challenges for the different analyses done in LSST. In this presentation, we will focus on two sources of systematic uncertainty: observational systematics and atmospheric conditions. For the former, we will explore the methods and lessons from the DES-Y3 galaxy clustering analysis, the ongoing work for Y6 and the prospects for LSST-DESC. For the latter, we will introduce LSST’s Auxiliary Telescope (AuxTel), whose purpose is to measure the atmospheric transparency and to derive color corrections based on spectroscopic observations.