Multiplicity among young and evolved stars is ubiquitous because stars are formed in clusters and associations. The presence of one or more close stellar companions can dramatically affect the fate of stellar systems, leading to a rich variety of astrophysical phenomena: type Ia supernovae, Ba stars, blue stragglers, heartbeat stars, etc. In addition, stellar multiplicity is a fundamental factor to consider for inferring the exoplanets demographics or the dark matter distribution in dwarf galaxies. Such binaries are best detected through their radial velocity variations by large on-going spectroscopic surveys. The Gaia-ESO survey is a ground-based spectroscopic survey, thought as a complement to the Gaia mission, in order to provide high accuracy radial velocities and chemical abundances for a hundred thousand stars. Among them we identified more than 1000 spectroscopic binaries with 1 to 4 visible components, most of them previously unknown due to their faint magnitudes. I will present the analysis of this binary sample and discuss its statistical properties as the distribution of the orbital periods and the dependence of the binary fraction with temperature and metallicity.

Abstract: Galaxy clusters are one of the most powerful cosmological tool. Their abundance as a function of cluster mass is sensitive to both the expansion history and the history of structure formation in the Universe. Various cluster observables such as X-ray luminosity, temperature and Sunyaev- Zel’dovich (SZ) effect have been shown to scale with cluster mass, therefore, can be used as a proxy of total cluster mass. We use Magneticum simulation setup to explore the cosmology dependence of galaxy cluster scaling relations which otherwise cannot be tested by observations. We run the same simulation set-up in fifteen different cosmological environments. Our simple, cosmology dependent mass-observable scaling relation parametrisation can be used to forecast the degeneracies between the amplitude of the scaling relation and the cosmological parameters as well as to explore the combination of potential probes to break these degeneracies.