We present Phantom, a fast, parallel, modular and low-memory smoothed particle hydrodynamics and magnetohydrodynamics code developed over the last decade for astrophysical applications in three dimensions. The code has been developed with a focus on stellar, galactic, planetary and high energy astrophysics and has already been used widely for studies of accretion discs and turbulence, from the birth of planets to how black holes accrete. Here we describe and test the core algorithms as well as modules for magnetohydrodynamics, self-gravity, sink particles, dust-gas mixtures, H2 chemistry, physical viscosity, external forces including numerous galactic potentials, Lense-Thirring precession, Poynting-Robertson drag and stochastic turbulent driving. Phantom is hereby made publicly available.

We present hydrodynamic simulations of the common envelope binary interaction between a giant star and a compact companion carried out with the adaptive mesh refinement code enzo and the smooth particle hydrodynamics code phantom. These simulations mimic the parameters of one of the simulations by Passy et al., but assess the impact of a larger, more realistic initial orbital separation on the simulation outcome. We conclude that for both codes the post-common envelope separation is somewhat larger and the amount of unbound mass slightly greater when the initial separation is wide enough that the giant does not yet overflow or just overflows its Roche lobe. phantom has been adapted to the common envelope problem here for the first time and a full comparison with enzo is presented, including an investigation of convergence as well as energy and angular momentum conservation. We also set our simulations in the context of past simulations. This comparison reveals that it is the expansion of the giant before rapid in-spiral and not spinning up of the star that causes a larger final separation. We also suggest that the large range in unbound mass for different simulations is difficult to explain and may have something to do with simulations that are not fully converged.

The Rotten Egg Nebula has at its core a binary composed of a Mira star and an A-type companion at a separation >10 au. It has been hypothesized to have formed by strong binary interactions between the Mira and a companion in an eccentric orbit during periastron passage ∼800 years ago. We have performed hydrodynamic simulations of an asymptotic giant branch star interacting with companions with a range of masses in orbits with a range of initial eccentricities and periastron separations. For reasonable values of the eccentricity, we find that Roche lobe overflow can take place only if the periods are ≪ 100 yr. Moreover, mass transfer causes the system to enter a common envelope phase within several orbits. Since the central star of the Rotten Egg nebula is an AGB star, we conclude that such a common envelope phase must have lead to a merger, so the observed companion must have been a tertiary companion of a binary that merged at the time of nebula ejection. Based on the mass and timescale of the simulated disc formed around the companion before the common envelope phase, we analytically estimate the properties of jets that could be launched. Allowing for super-Eddington accretion rates, we find that jets similar to those observed are plausible, provided that the putative lost companion was relatively massive.

We have simulated a common envelope interaction of a 0.88-M , 90-R , red giant branch star and a 0.6-M , compact companion with the smoothed particle hydrodynamics code, phantom, from the beginning of the Roche lobe overflow phase to the beginning of the self-regulated inspiral, using three different resolutions. The duration of the Roche lobe overflow phase is resolution dependent and would lengthen with increased resolution beyond the ∼20 years observed, while the inspiral phase and the post-common envelope separation are largely independent of resolution. Mass transfer rates through the Lagrangian points drive the orbital evolution during the Roche lobe overflow phase, as predicted analytically. The absolute mass transfer rate is resolution dependent, but always within an order of magnitude of the analytical value. Similarly, the gravitational drag in the simulations is close to the analytical approximation. This gives us confidence that simulations approximate reality. The L 2 and L 3 outflow observed during Roche lobe overflow remains bound, forming a circumbinary disk that is largely disrupted by the common envelope ejection. However, a longer phase of Roche lobe overflow and weaker common envelope ejection typical of a more stable binary may result in a surviving circumbinary disk. Finally, we examine the density distribution resulting from the interaction for simulations that include or omit the phase of Roche lobe overflow. We conclude that the degree of stability of the Roche lobe phase may modulate the shape of the subsequent planetary nebula, explaining the wide range of post-common envelope planetary nebula shapes observed.

We conduct three-dimensional hydrodynamic simulations of the common envelope binary interaction and show that if the companion were to launch jets while interacting with the giant primary star's envelope, the jets would remove a substantial fraction of the envelope's gas. We use the setup and numerical code of an earlier common envelope study that did not include jets, with a 0.88-M , 83-R red giant star and a 0.3-M companion. The assumption is that the companion star accretes mass via an accretion disk that is responsible for launching the jets which, in the simulations, are injected numerically. For the first time we conduct simulations that include jets as well as the gravitational energy released by the inspiraling core-companion system. We find that simulations with jets unbind approximately three times as much envelope mass than identical simulations that do not include jets, though the total fraction of unbound gas remains below 50% for these particular simulations. The jets generate high velocity outflows in the polar directions. The jets also increase the final corecompanion orbital separation and lead to a kick velocity of the core-companion binary system. Our results show that, if able to form, jets could play a crucial role in ejecting the envelope and in shaping the outflow.