Magnetic field amplification during the common envelope phase

Sebastian T. Ohlmann, Friedrich K. Röpke, Rüdiger Pakmor, Volker Springel, Ewald Müller
2016 Monthly Notices of the Royal Astronomical Society: Letters  
During the common envelope (CE) phase, a giant star in a binary system overflows its Roche lobe and unstable mass transfer leads to a spiral-in of the companion, resulting in a close binary system or in a merger of the stellar cores. Dynamo processes during the CE phase have been proposed as a mechanism to generate magnetic fields that are important for forming magnetic white dwarfs (MWDs) and for shaping planetary nebulae. Here, we present the first magnetohydrodynamics simulations of the
more » ... ical spiral-in during a CE phase. We find that magnetic fields are strongly amplified in the accretion stream around the 1M_ companion as it spirals into the envelope of a 2M_ RG. This leads to field strengths of 10 to 100 kG throughout the envelope after 120 d. The magnetic field amplification is consistent with being driven by the magnetorotational instability. The field strengths reached in our simulation make the magnetic field interesting for diagnostic purposes, but they are dynamically irrelevant. They are also too small to explain the formation of the highest fields found in MWDs, but may be relevant for luminous red novae, and detecting magnetic fields in these events would support the scenario as proposed here.
doi:10.1093/mnrasl/slw144 fatcat:kqe353saynbgreu4xfpuqxglt4