Common Envelope Evolution on a Moving Mesh

Abstract

We outline the methodology of simulating common envelope evolution (CEE) with the moving-mesh code MANGA. We extend MANGA to include multiple time-steps. This provides substantial speedups for problems with large dynamic range. We describe the implementation of realistic equations of state relevant in stellar structure and the generation of suitable initial conditions. We then carry out two example simulations of a 2 ${\mathrm{M}}_{\odot }$ red giant with a 0.36 ${\mathrm{M}}_{\odot }$ core and a 1 ${\mathrm{M}}_{\odot }$ companion undergoing CEE for 240 days. In one simulation the red giant is set into corotation with the orbital motion and in the other it is non-rotating. We find that the separation between the companion and red giant core shrinks from 52 ${\mathrm{R}}_{\odot }$ to 3.6 ${\mathrm{R}}_{\odot }$ and 3.2 ${\mathrm{R}}_{\odot }$ respectively, ending with an eccentricity of 0.1. We also find that 66 and 63 per cent of the envelope mass is ejected. This is higher than in many previous works. Several reasons for this are discussed. These include our inclusion of recombination energy. Our simulations show that putting giants in corotation increases the fraction of mass ejected from the system and results in a larger final orbital separation. We conclude that the entire envelope of the red giant might be ejected during the plunge phase of CEE in this region of parameter space.

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