L2 Puppis (also known as HD 56096) is a giant star in the constellation of Puppis and is located between the bright stars Canopus and Sirius. It is a semi-regular pulsating star. It is believed to be a binary system in transition to planetary nebulae.
In 2016, we studied the morphology and broad-band spectral-energy-distribution of L2 Puppis. In this research, we studied a possible way to have a circumbinary disk in an AGB binary system. We took L2 Puppis system as an example and proposed that a short period of high mass loss rate pulsation from the AGB star may lead to such morphology. Besides high mass loss rate, the pulsation should also have sub-escaping speed to let some of the pulsed material be gravitationally bound to the binary system. We used AstroBEAR to carry out the hydrodynamic simulation. Then we exported the data of the simulation and used RADMC3D to generate synthetic images and broad band SED. Full article can be found here.
|The figure on the top is the 3D volume rendering of the 3au simulation. The iframe on the bottom is the movies of our five simulations.|
AGB stars are large in size. They can lose mass via wind rapidly. When an AGB star is in a binary system, its wind can interact with the companion star (secondary). The ejected mass can be accreted by the secondary or remain gravitationally bound to the binary system or escape the binary system. Thus accretion discs and circumbinary discs may simultaneously exist in such systems.
To study the formation of discs and mass transfer in the binary systems that have AGB stars, we perform 3D radiation hydrodynamic simulation with AstroBEAR. Dust formation and molecular cooling are also taken into consideration. We carry out six simulations varying in the outflow, separation and mass ratio. In our closest binary simulations, our models exemplify the wind Roche lobe overflow while in our wide binary cases, the mass transfer exhibits Bondi-Hoyle accretion. The morphologies of the outflows in the binary systems are varied. The variety may provide clues to how the late AGB phase influences planetary nebulae shaping. To attain the highest computational efficiency and the most stable results, all simulations are run in the corotating frame. Full article can be found here.
Wind-accelerated orbital evolution in binary systems with giant stars(2017)
|amerge and abi are the binary separations that distinguish merge and not merge scenarios and moving closer and separating scenarios, respectively.|
Since AGB wind can transfer mass and angular momentum effectively. The orbital period and binary separation of the binary system will accordingly. What mechanisms are the important ones that can affect the binary orbit? How do they influence the binary evolution?
Using 3D radiation-hydrodynamic simulations and analytic theory, we study the orbital evolution of asymptotic-giant-branch (AGB) binary systems for various initial orbital separations and mass ratios, and thus different initial accretion modes. The time evolution of binary separations and orbital periods are calculated directly from the averaged mass loss rate, accretion rate and angular momentum loss rate. We separately consider spin-orbit synchronized and zero spin AGB cases. We find that the the angular momentum carried away by the mass loss together with the mass transfer can effectively shrink the orbit when accretion occurs via wind-Roche-lobe overflow. In contrast, the larger fraction of mass lost in Bondi-Hoyle-Lyttleton accreting systems acts to enlarge the orbit. Synchronized binaries tend to experience stronger orbital period decay in close binaries. We also find that orbital period decay is faster when we account for the nonlinear evolution of the accretion mode as the binary starts to tighten. This can increase the fraction of binaries that result in common envelope, luminous red novae, Type Ia supernovae and planetary nebulae with tight central binaries. The results also imply that planets in the the habitable zone around white dwarfs are unlikely to be found. Full article can be found here