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Binary star origin of high field magnetic white dwarfs

Tout, Christopher A; Wickramasinghe, Dayal; Liebert, James; Ferrario, Lilia; Pringle, James

Description

White dwarfs with surface magnetic fields in excess of 1 MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables (CVs). Some 1253 white dwarfs with a detached low-mass main-sequence companion are identified in the Sloan Digital Sky Survey (SDSS) but none of these is observed to show evidence for Zeeman splitting of hydrogen lines associated with a magnetic field in excess of 1 MG. If such high magnetic fields on white dwarfs result from the isolated...[Show more]

dc.contributor.authorTout, Christopher A
dc.contributor.authorWickramasinghe, Dayal
dc.contributor.authorLiebert, James
dc.contributor.authorFerrario, Lilia
dc.contributor.authorPringle, James
dc.date.accessioned2015-12-07T22:42:52Z
dc.identifier.issn0035-8711
dc.identifier.urihttp://hdl.handle.net/1885/24740
dc.description.abstractWhite dwarfs with surface magnetic fields in excess of 1 MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables (CVs). Some 1253 white dwarfs with a detached low-mass main-sequence companion are identified in the Sloan Digital Sky Survey (SDSS) but none of these is observed to show evidence for Zeeman splitting of hydrogen lines associated with a magnetic field in excess of 1 MG. If such high magnetic fields on white dwarfs result from the isolated evolution of a single star, then there should be the same fraction of high field magnetic white dwarfs among this SDSS binary sample as among single stars. Thus, we deduce that the origin of such high magnetic fields must be intimately tied to the formation of CVs. The formation of a CV must involve orbital shrinkage from giant star to main-sequence star dimensions. It is believed that this shrinkage occurs as the low-mass companion and the white dwarf spiral together inside a common envelope. CVs emerge as very close but detached binary stars that are then brought together by magnetic braking or gravitational radiation. We propose that the smaller the orbital separation at the end of the common envelope phase, the stronger the magnetic field. The magnetic CVs originate from those common envelope systems that almost merge. We propose further that those common envelope systems that do merge are the progenitors of the single high field magnetic white dwarfs. Thus, all highly magnetic white dwarfs, be they single stars or the components of magnetic CVs, have a binary origin. This hypothesis also accounts for the relative dearth of single white dwarfs with fields of 104-106 G. Such intermediate-field white dwarfs are found preferentially in CVs. In addition, the bias towards higher masses for highly magnetic white dwarfs is expected if a fraction of these form when two degenerate cores merge in a common envelope. Similar scenarios may account for very high field neutron stars. From the space density of single highly magnetic white dwarfs we estimate that about three times as many common envelope events lead to a merged core as to a CV.
dc.publisherBlackwell Publishing Ltd
dc.sourceMonthly Notices of the Royal Astronomical Society
dc.subjectKeywords: Binaries: close; Stars: magnetic fields; White dwarfs
dc.titleBinary star origin of high field magnetic white dwarfs
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume387
dc.date.issued2008
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationu4085724xPUB34
local.type.statusPublished Version
local.contributor.affiliationTout, Christopher A, University of Cambridge
local.contributor.affiliationWickramasinghe, Dayal, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationLiebert, James, University of Arizona
local.contributor.affiliationFerrario, Lilia, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationPringle, James, Cambridge Institute of Astronomy
local.description.embargo2037-12-31
local.bibliographicCitation.issue2
local.bibliographicCitation.startpage897
local.bibliographicCitation.lastpage901
local.identifier.doi10.1111/j.1365-2966.2008.13291.x
dc.date.updated2015-12-07T11:12:38Z
local.identifier.scopusID2-s2.0-45149084467
local.identifier.thomsonID000256688700038
CollectionsANU Research Publications

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