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Formation of high-field magnetic white dwarfs from common envelopes
Jason Nordhaus, Sarah Wellons, David S. Spiegel, Brian D. Metzger, Eric G. Blackman and Neta A. Bahcall
Proceedings of the National Academy of Sciences of the United States of America
Vol. 108, No. 8 (February 22, 2011), pp. 3135-3140
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/41060894
Page Count: 6
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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-mainsequence 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.
Proceedings of the National Academy of Sciences of the United States of America © 2011 National Academy of Sciences