Theory of stellar mass loss and its implications: from binary stars to magnetars
Stars can lose mass in various ways, significantly shaping their evolution and driving diverse astrophysical phenomena. In this seminar, I will talk about models of stellar mass loss that my collaborators and I developed in two distinct settings. First, we proposed a theory of mass transfer in binary stars, treating the Roche potential as a converging nozzle that channels material through the inner Lagrange point. In the sub-Eddington regime, our model yields mass-transfer rates similar to standard prescriptions (within a factor of a few). Including radiative effects, our model shows that radiation enhances mass transfer from underfilling, radiation-dominated envelopes. Additionally, super-Eddington, convectively inefficient layers can drive high mass-transfer rates even before Roche-lobe overflow, potentially explaining outbursts resembling those of Luminous Blue Variables. Second, we introduced a model of mass ejection in magnetar giant flares, energetic bursts from highly magnetized neutron stars. Motivated by the radio afterglow of the 2004 giant flare from the magnetar SGR 1806-20, we modeled how sudden magnetic dissipation forms a high-pressure shell that shock-heats and ejects part of the magnetar crust. Analytical estimates and relativistic hydrodynamic simulations show that the ejecta meet conditions for heavy-element rapid neutron-capture (r-process) nucleosynthesis. The subsequent decay powers a brief (~10--15 min), luminous (~10^39--10^40 erg/s) optical/UV kilonova-like transient, a “nova brevis” (brief/short nova). Additionally, radioactive decay releases Doppler-broadened gamma-ray lines, forming a quasi-continuous spectrum. This emission, rising ~10 min post-flare and fading over hours, matches an unexplained gamma-ray signal following the December 2004 giant flare, providing direct observational evidence for r-process element synthesis in magnetar giant flares.