We research interacting binary stars, with a special focus on post-interaction systems that include exposed stellar cores, that is, envelope-stripped helium stars. Our main computational tools include the binary stellar evolution code MESA (Paxton et al. 2011, 2013, 2015, 2018, 2019, Jermyn et al. 2023), the non-LTE radiative transfer code CMFGEN (Hillier 1990, Hillier & Miller 1998, Hillier 2012), and the spectral population synthesis code MOSS especially made for stripped stars (Götberg et al. 2019, 2020a, 2020b, Hovis-Afflerbach et al. 2025). We also use photometric and spectroscopic observational data to explore the physics of binary stars (e.g., Drout & Götberg et al. 2023, Götberg et al. 2023).