title: Formation of high-field magnetic white dwarfs from common envelopes.
abstract: The origin of highly magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, such as a planet, brown dwarf, or low-mass star, is engulfed by a post-main-sequence giant, gravitational torques in the envelope of the giant lead to a reduction of the companion's orbit. Sufficiently low-mass companions in-spiral until they are shredded by the strong gravitational tides near the white dwarf core. Subsequent formation of a super-Eddington accretion disk from the disrupted companion inside a common envelope can dramatically amplify magnetic fields via a dynamo. Here, we show that these disk-generated fields are sufficiently strong to explain the observed range of magnetic field strengths for isolated, high-field magnetic white dwarfs. A higher-mass binary analogue may also contribute to the origin of magnetar fields.
authors.affiliation: Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA. nordhaus@astro.princeton.edu
authors.forename: Jason
authors.initials: J
authors.lastname: Nordhaus
authors.forename: Sarah
authors.initials: S
authors.lastname: Wellons
authors.forename: David S
authors.initials: DS
authors.lastname: Spiegel
authors.forename: Brian D
authors.initials: BD
authors.lastname: Metzger
authors.forename: Eric G
authors.initials: EG
authors.lastname: Blackman