The EREBOS project: Studying the influence of substellar objects on late stellar evolution

Planets and brown dwarfs in close orbits will interact with their host stars, as soon as they evolve to become red giants, which can lead to the loss of the envelope of the host star. However, the outcome of those interactions is still unclear. Recently, several brown dwarfs have been discovered orbiting hot subdwarf stars in very short orbital periods of 0.065 - 0.096 d. More than 6% of those stars might have close substellar companions. This shows that such companions can significantly affect late stellar evolution and that sdB binaries are ideal objects to study this influence. More than a hundred new eclipsing sdB binary systems with cool low-mass companions with periods from 0.05 to 0.5 d were discovered based on their lightcurves by the OGLE and ATLAS project. We want to use this unique and homogeneously selected sample to derive the mass distribution of the companions, constrain the fraction of substellar companions and determine the minimum mass needed to strip of the red-giant envelope. Therefore, we started the EREBOS (Eclipsing Reflection Effect Binaries from the OGLE Survey), which aims at analyzing as many of the newly discovered HW Vir systems as possible based on a spectroscopic and photometric follow-up of all targets. For this we were granted with an ESO Large Program for ESO/VLT-FORS. Here we will introduce the project and give the current status together with the first results.