The<i>Gaia</i>-ESO Survey: the selection function of the Milky Way field stars

Abstract

The Gaia-ESO Survey was designed to target all major Galactic components\n(i.e., bulge, thin and thick discs, halo and clusters), with the goal of\nconstraining the chemical and dynamical evolution of the Milky Way. This paper\npresents the methodology and considerations that drive the selection of the\ntargeted, allocated and successfully observed Milky Way field stars. The\ndetailed understanding of the survey construction, specifically the influence\nof target selection criteria on observed Milky Way field stars is required in\norder to analyse and interpret the survey data correctly. We present the target\nselection process for the Milky Way field stars observed with VLT/FLAMES and\nprovide the weights that characterise the survey target selection. The weights\ncan be used to account for the selection effects in the Gaia-ESO Survey data\nfor scientific studies. We provide a couple of simple examples to highlight the\nnecessity of including such information in studies of the stellar populations\nin the Milky Way.\n