Wobbling Jets in Common Envelope Evolution

We find that the convective motion in the envelopes of red supergiant (RSG) stars supplies a non-negligible stochastic angular momentum to the mass that a secondary star accretes in a common envelope evolution (CEE), such that jets that the secondary star launches wobble. The orbital motion of the secondary star in a CEE and the density gradient in the envelope impose a nonzero angular momentum to the accreted mass with a constant direction parallel to the orbital angular momentum. From one-dimensional stellar evolution simulations with the numerical code mesa we find that the stochastic convection motion in the envelope of RSG stars adds a stochastic angular momentum component with an amplitude that is about 0.1-1 times that of the constant component due to the orbital motion. We mimic a CEE of the RSG star by removing envelope mass at a high rate and by depositing energy into its envelope. The stochastic angular momentum implies that the accretion disk around the secondary star (which we do not simulate), and therefore the jets that it launches, wobble with angles of up to tens of degrees with respect to the orbital angular momentum axis. This wobbling makes it harder for jets to break out from the envelope and can shape small bubbles in the ejecta that compress filaments that appear as arcs in the ejected nebula, i.e., in planetary nebulae when the giant is an asymptotic giant branch star.

Automated summary

We have found that the convective motion in the envelopes of red supergiant (RSG) stars contributes a significant stochastic angular momentum to the mass accreted by a secondary star in a common envelope evolution (CEE), causing the wobbling of the jets launched by the secondary star. Through stellar evolution simulations, we have determined that the stochastic convection motion in the RSG envelope adds a random component to the angular momentum of the accreted mass, which is about 0.1-1 times the constant component due to the orbital motion. This stochastic angular momentum leads to the wobbling of the accretion disk and jets, making it more difficult for them to break out from the envelope and shaping small bubbles in the ejected nebula.