Energy Budget and Core-Envelope Motion in Common Envelope Evolution. (arXiv:1812.11196v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Chamandy_L/0/1/0/all/0/1">Luke Chamandy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tu_Y/0/1/0/all/0/1">Yisheng Tu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blackman_E/0/1/0/all/0/1">Eric G. Blackman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carroll_Nellenback_J/0/1/0/all/0/1">Jonathan Carroll-Nellenback</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Frank_A/0/1/0/all/0/1">Adam Frank</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_B/0/1/0/all/0/1">Baowei Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nordhaus_J/0/1/0/all/0/1">Jason Nordhaus</a>
We analyze a 3D hydrodynamic simulation of common envelope evolution to
understand how energy is transferred between various forms, leading to the
partial unbinding of the envelope. We find that $13$-$14%$ of the envelope is
unbound during the simulation. Virtually all of the unbinding occurs before the
end of the rapid plunge-in phase, here defined to coincide with the first
periastron passage. In contrast, the total envelope energy is nearly constant
during this time because positive energy transferred to the gas is
counterbalanced by the negative binding energy from the closer proximity of the
inner layers to the plunged-in secondary. During the subsequent slow spiral-in
phase, energy continues to transfer to the envelope from the red giant core and
secondary core particles. In our analysis, we critically assess the commonly
used $alpha_mathrm{CE}$-energy formalism, and suggest an alternative that
more cleanly separates core particles and gas. Applying this formalism, we
discuss that overcoming current limitations of existing simulations with
respect to both the accessible parameter regime and the giant model may enable
complete envelope ejection from orbital evolution even without new energy
sources. We also propose that relative motion between the centre of mass of the
envelope and the centre of mass of the particles could account for the offsets
of planetary nebula central stars from the nebula’s geometric centre.
We analyze a 3D hydrodynamic simulation of common envelope evolution to
understand how energy is transferred between various forms, leading to the
partial unbinding of the envelope. We find that $13$-$14%$ of the envelope is
unbound during the simulation. Virtually all of the unbinding occurs before the
end of the rapid plunge-in phase, here defined to coincide with the first
periastron passage. In contrast, the total envelope energy is nearly constant
during this time because positive energy transferred to the gas is
counterbalanced by the negative binding energy from the closer proximity of the
inner layers to the plunged-in secondary. During the subsequent slow spiral-in
phase, energy continues to transfer to the envelope from the red giant core and
secondary core particles. In our analysis, we critically assess the commonly
used $alpha_mathrm{CE}$-energy formalism, and suggest an alternative that
more cleanly separates core particles and gas. Applying this formalism, we
discuss that overcoming current limitations of existing simulations with
respect to both the accessible parameter regime and the giant model may enable
complete envelope ejection from orbital evolution even without new energy
sources. We also propose that relative motion between the centre of mass of the
envelope and the centre of mass of the particles could account for the offsets
of planetary nebula central stars from the nebula’s geometric centre.
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