Radiation pressure and equation of state are important in the envelope unbinding process in common envelope evolution
Authors
Zhuo Chen
Abstract
In common envelope evolution, the ultimate unbinding of the envelope during the plunge-in phase involves complex and poorly understood physical processes that may give rise to luminous red novae. In this work, we investigate the roles of radiation and gas pressures in envelope unbinding. We perform a parameter space survey using a one-dimensional radiation hydrodynamic model that is solved by {\tt Guangqi} to study the impact of key parameters on the mass unbound fraction and resulting light curves. The parameters include the radiation to gas energy ratio $\mathcal{E}/e_{\text{g}}\in[0.2,3.2]$, speed of the ejecta, ranging from 70\% to 85\% of the escape velocity, and equation of state (EoS). For comparison, we also perform simulations with pure hydrodynamic or no radiation pressure effect conditions. Our simulations demonstrate that the radiation pressure is crucial for the envelope unbinding. Specifically, the radiation pressure may dominate in a high opacity and high luminosity layer just below the recombination front, where it can accelerate the sub-escape material to escape velocities. A realistic EoS further enhances the pressure gradient, especially during the early phase of ejection at small radii, promoting additional envelope ejection. Both $\mathcal{E}/e_{\text{g}}$ and EoS significantly alter light curve shapes, and provide observable diagnostics for these processes. We show that the relative energy error of all the simulations is no more than 1.4\%, and all the simulations are close to convergence.
