Binary star origin of high field magnetic white dwarfs

By C. Tout, D. Wickramasinghe, J. Liebert, L. Ferrario, J. E. Pringle. 2008

171 citations recorded by the source corpus.

White dwarfs with surface magnetic fields in excess of 1MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables. Some 1,253 white dwarfs with a detached low-mass main-sequence companion are identified in the Sloan Digital Sky Survey but none of these is observed to show evidence for Zeeman splitting of hydrogen lines associated with a magnetic field in excess of 1MG. 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 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 cataclysmic variables. 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 lowmass 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 cataclysmic variables 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 white dwarfs. Thus all highly magnetic white dwarfs, be they single stars or the components of MCVs, have a binary origin. This hypothesis also accounts for the relative dearth of single white dwarfs with fields of 10 4 10 6 G. Such intermediate-field white dwarfs are found preferentially in cataclysmic variables. 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 cataclysmic variable.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/1c2ff97577cbc9613835649b4d7d7402979ceccc

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Citations in the corpus

Magnetic white dwarf stars in the Sloan Digital Sky Survey (2012, background): “With the low resolution (R ≃ 2 000) of the SDSS spectra, magnetic fields weaker than 2 MG are only detectable for the highest S/N spectra (e.g. Tout et al. 2008).”
THE INCIDENCE OF STELLAR MERGERS AND MASS GAINERS AMONG MASSIVE STARS (2013, background): “(d) It has been suggested that a merger process may lead to the generation of a magnetic field (e.g. Tout et al. 2008; Ferrario et al. 2009).”
Common envelope evolution: where we stand and how we can move forward (2012, background): “A large-scale α − Ω dynamo during CEE has been argued to produce compact remnants with large magnetic moments (Tout et al. 2008; Potter and Tout 2010).”
Magnetic White Dwarfs (2015, background): “However, as Tout et al. (2008) have pointed out, WDs cool down to an effective temperature of 15, 000K in only ∼ 107 years and at a period of 2 h, the orbital decay time scale due to gravitational wave radiation is about 3× 109 years which is sufficient for a WD to cool down considerably and reach…”
Observational Clues to the Progenitors of Type Ia Supernovae (2013, background): “Nordhaus et al. (2011), Tout et al. (2008) and Garćıa-Berro et al. (2012) have argued that strong magnetic fields in WDs are always the result of binary interactions, be it through accretion, common-envelope evolution, or mergers.”