3D MHD Simulations of Mass Loss Immediately Before Common-Envelope Onset

Red giants and red supergiants, can undergo strong binary interactions when they fill their Roche lobes, potentially leading to the onset of a common-envelope (CE) phase or a stellar merger. Luminous red novae (LRNe) are widely interpreted as observational counterparts of such events. Their light curves can be powered by shocks between fast ejecta and pre-existing circumbinary material. In current models, this material is set by assumed prescriptions for pre-dynamical mass loss, still largely unconstrained by multidimensional simulations. With the upcoming Rubin Observatory LSST sample, physically grounded models for pre-CE mass loss are essential. Here, we perform three-dimensional MHD simulations of binaries immediately before CE to test pre-CE mass-transfer prescriptions and characterize the resulting circumbinary environment.