News from the EREBOS project

TL;DR

The EREBOS project investigates close binary systems with hot subdwarfs and low-mass companions to understand their formation, evolution, and the role of sub-stellar objects like hot Jupiters, using data from the OGLE survey and ESO follow-up.

Contribution

This study introduces the EREBOS project, providing a large, homogeneous sample of eclipsing sdB binaries to analyze companion mass distribution and test models of planetary influence on stellar evolution.

Findings

Discovery of 38 new eclipsing sdB binaries from OGLE data.

Identification of 75 additional systems in the Galactic bulge.

Initial constraints on the mass distribution of low-mass companions.

Abstract

Planets and brown dwarfs in close orbits will interact with their host stars, as soon as the stars evolve to become red giants. However, the outcome of those interactions is still unclear. Recently, several brown dwarfs have been discovered orbiting hot subdwarf stars at very short orbital periods of 0.065 - 0.096 d. More than 8\% of the close hot subdwarf binaries might have sub-stellar companions. This shows that such companions can significantly affect late stellar evolution and that sdB binaries are ideal objects to study this influence. Thirty-eight new eclipsing sdB binary systems with cool low-mass companions and periods from 0.05 to 0.5 d were discovered based on their light curves by the OGLE project. In the recently published catalog of eclipsing binaries in the Galactic bulge, we discovered 75 more systems. We want to use this unique and homogeneously selected sample to derive the mass distribution of the companions, constrain the fraction of sub-stellar companions and determine the minimum mass needed to strip off the red-giant envelope. We are especially interested in testing models that predict hot Jupiter planets as possible companions. Therefore, we started the EREBOS (Eclipsing Reflection Effect Binaries from the OGLE Survey) project, which aims at analyzing those new HW Vir systems based on a spectroscopic and photometric follow up. For this we were granted an ESO Large Program for ESO-VLT/FORS2. Here we give an update on the current status of the project and present some preliminary results.