The origin of isolated white dwarfs (WDs) with magnetic fields in excess of ∼1 MG has remained a mystery since their initial discovery. Recently, the formation of these high-field magnetic WDs has been observationally linked to binary interactions with low-mass companions (< 0.1 solar mass ) during post- main-sequence evolution. Planetary and M dwarf companions orbiting within several AU of main-sequence stars will become engulfed during the primary’s expansion off the main sequence. Such low-mass companions rapidly in-spiral inside a “common envelope” until they are tidally disrupted near the natal white dwarf core. Formation of an accretion disk from the shredded companion provides a source of turbulence and shear which, in principle, acts to amplify magnetic fields and transport them to the WD surface. However, the disk is initially very cold (∼ 10^3 K) compared to the hot thermal bath present in the center of the red giant (∼ 10^7 K). As there is significant shear in the system, entrainment of hot stellar material into the cold disk may lead to vigorous mixing and thermal evaporation before the field can be sufficiently amplified. To study the evolution and lifetime of the tidally-disrupted disks, we perform three-dimensional hydrodynamic simulations of accretion disks formed from 1, 3, 6 and 10 Jupiter mass planets. While entrainment leads to a decrease in disk mass, we find that all disks survive long enough to sufficiently amplify the magnetic field.
Astrophysical Sciences and Technology (MS)
Department, Program, or Center
School of Physics and Astronomy (COS)
Guidarelli, Gabriel Colin, "Accretion disks formed from tidally-disrupted companions inside AGB stars" (2018). Thesis. Rochester Institute of Technology. Accessed from
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