Magnetic white dwarf stars in the Sloan Digital Sky Survey

Kepler, S. O.; Pelisoli, Ingrid; Jordan, S.; Kleinman, S. J.; Koester, D.; Külebi, Baybars; Peçanha, Viviane; Castanheira, B. G.; Nitta, A.; Costa, J. E. S.; Winget, D. E.; Kanaan, A.; Fraga, L.

doi:10.1093/mnras/sts522

Cited by 180 publications

(185 citation statements)

References 53 publications

(57 reference statements)

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“…The range we obtained for such frequencies falls between the infrared and UV bands. It is important to remark that magnetic fields in white dwarfs ranging from 10 7 G up to 10 9 G are routinely observed; see, e.g., Külebi et al (2009), Külebi et al (2010a), Kepler et al (2010), and very recently Kepler et al (2013), where from the Data Release 7 of the Sloan Digital Sky Survey, white dwarfs with magnetic fields in the range from around 10 6 G to 7.3×10 8 G have been found from the analysis of the Zeeman splitting of the Balmer absorption lines. Deep photometric and spectrometric observations in the range of cyclotron frequencies predicted in this work are therefore highly recommended to detect possible absorptions and line-splitting features in the spectra of SGRs and AXPs.…”

Section: Discussionmentioning

confidence: 94%

“…It is remarkable that white dwarfs with large magnetic fields from 10 7 G all the way up to 10 9 G have been indeed observed (see e.g., Külebi et al 2009Külebi et al , 2010aKepler et al 2010Kepler et al , 2013. Also, most of the observed magnetized white dwarfs are massive; e.g., REJ 0317-853 with M ∼ 1.35 M and B ∼ (1.7−6.6) × 10 8 G (Barstow et al 1995;Külebi et al 2010b); PG 1658+441 with M ∼ 1.31 M and B ∼ 2.3 × 10 6 G (Liebert et al 1983;Schmidt et al 1992); and PG 1031+234 with the highest magnetic field ∼10 9 G (Schmidt et al 1986;Külebi et al 2009).…”

Section: Introductionmentioning

confidence: 99%

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SGR 0418+5729,SwiftJ1822.3-1606, and 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs

Boshkayev

Izzo

Rueda

et al. 2013

A&A

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Aims. We describe the so-called low magnetic field magnetars, SGR 0418+5729, Swift J1822.3-1606, and the AXP prototype 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs. Methods. We give bounds for the mass, radius, moment of inertia, and magnetic field for these sources by requesting the stability of realistic, general relativistic, uniformly rotating white dwarfs. We also present the theoretical expectation of the infrared, optical, and ultraviolet emission of these objects and show their consistency with the current available observational data. Results. We improve the theoretical prediction of the lower limit of the spindown rate of SGR 0418+5729; for a white dwarf close to its maximum stable mass we obtain the very stringent interval for the spindown rate of 4.1 × 10 −16 <Ṗ < 6 × 10 −15 , where the upper value is the known observational limit. A lower limit has been also set for Swift J1822.3-1606, whose spindown rate is not yet fully confirmed. Our model provides for the sourceṖ ≥ 2.13 × 10 −15 if the star is close to its maximum stable mass. We give in addition the frequencies at which absorption features could be present in the spectrum of these sources as the result of the scattering of photons with the quantized electrons by the surface magnetic field.Key words. stars: magnetic field -stars: rotation -white dwarfs -stars: magnetars IntroductionSoft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are a class of compact objects that show interesting observational properties (see, e.g., Mereghetti 2008): rotational periods in the range P ∼ (2−12) s, spindown ratesṖ ∼ (10 −13 -10 −10 ), strong outburst of energies ∼(10 41 −10 43 ) erg, and in the case of SGRs, giant flares of even large energies ∼(10 44 -10 47 ) erg.The most popular model for the description of SGRs and AXPs, the magnetar model, is based on a neutron star of fiducial parameters M = 1.4 M , R = 10 km, and a moment of inertia I = 10 45 g cm 2 . It needs a neutron star magnetic field larger than the critical field for vacuum polarization B c = m 2 e c 3 /(e ) = 4.4 × 10 13 G in order to explain the observed X-ray luminosity in terms of the release of magnetic energy (Duncan & Thompson 1992; Thompson & Duncan 1995). There exist in the literature other models still based on neutron stars but of ordinary fields B ∼ 10 12 G; these models involve either the generation of drift waves in the magnetosphere or the accretion of fallback material via a circumstellar disk (see Malov 2010;Trümper et al. 2013, respectively, and references therein).Turning to the experimental point of view, the observation of SGR 0418+5729 with a rotational period of P = 9.08 s, an upper limit of the first time derivative of the rotational perioḋ P < 6.0 × 10 −15 (Rea et al. 2010), and an X-ray luminosity of L X = 6.2 × 10 31 erg s −1 can be considered as the Rosetta Stone for alternative models of SGRs and AXPs. The inferred upper limit of the surface magnetic field of SGR 0418+5729, B < 7.5 × 10 12 G; which describes it as a neutr...

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Section: Discussionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

SGR 0418+5729,SwiftJ1822.3-1606, and 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs

Boshkayev

Izzo

Rueda

et al. 2013

A&A

View full text Add to dashboard Cite

show abstract

“…Some 10-20% of WDs have surface magnetic fields B 10 kG, and about 5% have B 1 MG (Kawka et al 2007;Holberg et al 2008;Kepler et al 2013). Magnetic fields can be estimated from Zeeman-splitting of absorption-line cores, or by spectropolarimetric measurements of circular polarization variations across line profiles.…”

Section: Wd Rotationmentioning

confidence: 99%

Kepler and the seven dwarfs: detection of low-level day-time-scale periodic photometric variations in white dwarfs

Maoz

Mazeh

McQuillan

2014

Monthly Notices of the Royal Astronomical Society

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We make use of the high photometric precision of Kepler to search for periodic modulations among 14 normal (DA-and DB-type, likely non-magnetic) hot white dwarfs (WDs). In five, and possibly up to seven of the WDs, we detect periodic, ∼ 2 hr to 10 d, variations, with semi-amplitudes of 60-2000 ppm, lower than ever seen in WDs. We consider various explanations: WD rotation combined with magnetic cool spots; rotation combined with magnetic dichroism; rotation combined with hot spots from an interstellar-medium accretion flow; transits by size ∼ 50-200 km objects; relativistic beaming due to reflex motion caused by a cool companion WD; or reflection/reradiation of the primary WD light by a brown-dwarf or giant-planet companion, undergoing illumination phases as it orbits the WD. Each mechanism could be behind some of the variable WDs, but could not be responsible for all five to seven variable cases. Alternatively, the periodicity may arise from UV metal-line opacity, associated with accretion of rocky material, a phenomenon seen in ∼ 50% of hot WDs. Nonuniform UV opacity, combined with WD rotation and fluorescent optical re-emission of the absorbed UV energy, could perhaps explain our findings. Even if reflection by a planet is the cause in only a few of the seven cases, it would imply that hot Jupiters are very common around WDs. If some of the rotation-related mechanisms are at work, then normal WDs rotate as slowly as do peculiar WDs, the only kind for which precise rotation measurements have been possible to date.

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“…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%

“…Many of the known magnetic white dwarfs have been found recently from the Sloan Digital Sky Survey (SDSS, Kepler et al 2013). This survey (and most other surveys for white dwarfs) have been carried out using low resolution (and frequently low S/N) spectroscopy.…”

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 dwarf stars in the Sloan Digital Sky Survey

Cited by 180 publications

References 53 publications

SGR 0418+5729,SwiftJ1822.3-1606, and 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs

SGR 0418+5729,SwiftJ1822.3-1606, and 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs

Kepler and the seven dwarfs: detection of low-level day-time-scale periodic photometric variations in white dwarfs

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

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