Magnetic White Dwarfs

Ferrario, Lilia; Martino, D. de; Gänsicke, B. T.

doi:10.1007/s11214-015-0152-0

Cited by 338 publications

(403 citation statements)

References 459 publications

(260 reference statements)

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“…Hailey et al (2016) argue that the excess B-star population needed to explain high WD masses is within the large uncertainty of the expected population in the GC region. On the other hand, the average mass of the WD in the nonmagnetic CVs or isolated magnetic WDs are about 0.8M e (Ferrario et al 2015;Wijnen et al 2015). In addition, there is no clear evidence for high mass progenitors for the WDs in CVs (Zorotovic et al 2011).…”

Section: ) (A-mentioning

confidence: 97%

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

Hong

Mori

Hailey

et al. 2016

ApJ

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We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg 2 region around SgrA * with a total exposure of 1.7 Ms, and 7 sources in the SgrB2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ∼4× and ∼8×10 32 erg s -1 at the GC (8 kpc) in the 3-10 and 10-40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the SgrA diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%-60%). Both spectral analysis and logN-logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT>20 keV on average for a single temperature thermal plasma model or an average photon index of Γ=1.5-2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.

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Section: ) (A-mentioning

confidence: 97%

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

Hong

Mori

Hailey

et al. 2016

ApJ

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“…Some of them have measurable magnetic fields with strengths ranging from 10 3 to 10 9 G (Ferrario et al 2015). The incidence of magnetism is a matter of debate.…”

Section: Introductionmentioning

confidence: 99%

A Common Origin of Magnetism from Planets to White Dwarfs

Isern

Garcı́a–Berro

Külebi

et al. 2017

ApJL

111

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Isolated magnetic white dwarfs have field strengths ranging from kilogauss to gigagauss. However, the origin of the magnetic field has not been hitherto elucidated. Whether these fields are fossil, hence the remnants of original weak magnetic fields amplified during the course of the evolution of their progenitor stars, or are the result of binary interactions, or, finally, they are produced by other internal physical mechanisms during the cooling of the white dwarf itself, remains a mystery. At sufficiently low temperatures, white dwarfs crystallize. Upon solidification, phase separation of its main constituents, 12 C and 16 O, and of the impurities left by previous evolution occurs. This process leads to the formation of a Rayleigh-Taylor unstable liquid mantle on top of a solid core. This convective region, as it occurs in solar system planets like the Earth and Jupiter, can produce a dynamo able to yield magnetic fields of strengths of up to 0.1 MG, thus providing a mechanism that could explain magnetism in single white dwarfs.

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“…The most recent list, from Ferrario et al (2015), contains 15 white dwarfs which are supposed to have magnetic fields below about 120 kG. Our list in Table 2 contains only seven stars.…”

Section: Discussionmentioning

confidence: 99%

“…On the basis of many recent observations, we now know something about the occurrence of magnetic fields in most of the main stages of stellar evolution, from the pre-main sequence (Donati & Landstreet 2009;Hussain 2012;Alecian et al 2013) through the main sequence (Donati & Landstreet 2009;Petit et al 2013;Wade & MiMeS Collaboration 2015), the red giant (Aurière et al 2015) and asymptotic giant (Grunhut et al 2010) stages, and finally the white dwarf stage (Kepler et al 2013;Ferrario et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Discovery of an extremely weak magnetic field in the white dwarf LTT 16093 = WD 2047+372

Landstreet

Bagnulo

Martín

et al. 2016

A&A

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Context. Magnetic fields have been detected in several hundred white dwarfs, with strengths ranging from a few kG to several hundred MG. Only a few of the known fields have a mean magnetic field modulus below about 1 MG. Aims. We are searching for new examples of magnetic white dwarfs with very weak fields, and trying to model the few known examples. Our search is intended to be sensitive enough to detect fields at the few kG level. Methods. We have been surveying bright white dwarfs for very weak fields using spectropolarimeters at the Canada-France-Hawaii telescope, the William Herschel Telescope (WHT), the European Southern Observatory, and the Russian Special Astrophysical Observatory. We discuss in some detail tests of the WHT spectropolarimeter ISIS using the known magnetic strong-field Ap star HD 215441 (Babcock's star) and the long-period Ap star HD 201601 (γ Equ). Results. We report the discovery of a field with a mean field modulus of about 57 kG in the white dwarf LTT 16093 = WD 2047+372. The field is clearly detected through the Zeeman splitting of Hα seen in two separate circularly polarised spectra from two different spectropolarimeters. Zeeman circular polarisation is also detected, but only barely above the 3σ level. Conclusions. The discovery of this field is significant because it is the third weakest field ever unambiguously discovered in a white dwarf, while still being large enough that we should be able to model the field structure in some detail with future observations.

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Magnetic White Dwarfs

Cited by 338 publications

References 459 publications

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

A Common Origin of Magnetism from Planets to White Dwarfs

Discovery of an extremely weak magnetic field in the white dwarf LTT 16093 = WD 2047+372

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