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Numerical Simulations of Mass Transfer in Close and Contact Binaries Using Bipolytropes

By Kundan Vaman Kadam


We present the first self-consistent, three dimensional study of hydrodynamic simulations of mass transfer in close and contact binary systems, with both stars represented as bipolytropes (composite polytopes). The project is motivated by the recent eruption of V1309 Scorpii which was proved to be the merger of a contact binary system. The final eruption is assumed to be the disruption of the core of the secondary inside the more massive star. The initial, equilibrium binary models are rotating synchronously in circular orbits and are obtained using the Bipolytropic Self Consistent Field (BSCF) technique, which is a modi cation of Hachisu\u27s Self Consistent Field (HSCF) method. Both stars have a fully resolved core and envelope structure where the difference in equation of state is represented by different polytropic indices and the difference in composition is represented as the ratio of the average molecular weights. The validity of the BSCF method is confirmed by constructing single, rapidly rotating stars and toroidal disks and comparing their properties with well established numerical as well as analytical results. We simulate mass transfer and mergers of bipolytropic binary systems using two fully three-dimensional grid-based Eulerian codes, Flow-ER and Octotiger, at two different resolutions. We discuss the suitability of both the codes to simulate bipolytropic stellar binaries faithfully. The simulations conducted using the Flow-ER code show certain numerical artifacts due to the limited resolving capacity of the implemented fixed cylindrical grid. We compare the results of these simulations with ones carried out using Octotiger with Adaptive Mesh Refinement (AMR) capabilities, where most of the limitations have been improved upon. The initial conditions for each simulation across the codes are chosen to match as closely as possible so that the simulations can be used as benchmarks. Although there are some key differences, the detailed comparison of the simulations suggests that there is remarkable agreement between the results obtained using the two codes. With the comparison across the resolutions, we found that both the hydrodynamic codes are convergent. This study enables us to confidently simulate mass transfer and merger scenarios of binary systems involving bipolytropic components

Topics: luminous red novae, simulations, composite polytropes, bipolytropes, polytropes, simulations, astronomy, astrophysics, stars, binaries, binary stars, mass transfer, nova, equation of state, hydrodynamics, numerical methods, self consistent field technique, Physical Sciences and Mathematics
Publisher: LSU Digital Commons
Year: 2017
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