X-ray orbital modulation of a white dwarf accreting from an L dwarf

Stelzer, B.; Martino, D. de; Casewell, Sarah L.; Wynn, G. A.; Roy, Mervyn

doi:10.1051/0004-6361/201630038

Cited by 22 publications

(11 citation statements)

References 33 publications

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“…The accretion rates in period-bounce systems are low enough that they could appear similar to detached systems. There is some evidence from X-ray observations that SDSS J1212+0136 may be Roche-lobe filling (Stelzer et al 2017), which lends support to this interpretation. Therefore, these systems may form a distinct population from the longer period detached magnetic white dwarf binaries that have been the focus of this paper.…”

Section: Evolutionary Statusmentioning

confidence: 80%

Magnetic white dwarfs in post-common-envelope binaries

Parsons

Gänsicke

Schreiber

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Magnitude-limited samples have shown that 20-25 per cent of cataclysmic variables contain white dwarfs with magnetic fields of Mega Gauss strength, in stark contrast to the approximately 5 per cent of single white dwarfs with similar magnetic field strengths. Moreover, the lack of identifiable progenitor systems for magnetic cataclysmic variables leads to considerable challenges when trying to understand how these systems form and evolve. Here we present a sample of six magnetic white dwarfs in detached binaries with low-mass stellar companions where we have constrained the stellar and binary parameters including, for the first time, reliable mass estimates for these magnetic white dwarfs. We find that they are systematically more massive than non-magnetic white dwarfs in detached binaries. These magnetic white dwarfs generally have cooling ages of more than 1 Gyr and reside in systems that are very close to Roche-lobe filling. Our findings are more consistent with these systems being temporarily detached cataclysmic variables, rather than pre-cataclysmic binaries, but we cannot rule out the latter possibility. We find that these systems can display unusual asymmetric light curves that may offer a way to identify them in larger numbers in future. Seven new candidate magnetic white dwarf systems are also presented, three of which have asymmetric light curves. Finally, we note that several newly identified magnetic systems have archival spectra where there is no clear evidence of magnetism, meaning that these binaries have been previously missed. Nevertheless, there remains a clear lack of younger detached magnetic white dwarf systems.

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Section: Evolutionary Statusmentioning

confidence: 80%

Magnetic white dwarfs in post-common-envelope binaries

Parsons

Gänsicke

Schreiber

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…In the case of SDSS J1212+0136, early studies suggested that the brown dwarf was under filling its Roche lobe and was more likely to be a PREP than a LARP (Schmidt et al 2005;Farihi et al 2008). However, the X-ray observations of Stelzer et al (2017) strongly suggest that this system may be filling its Roche lobe and should be considered a LARP.…”

Section: Discussionmentioning

confidence: 99%

The magnetic system SMSS J1606-1000 as a period bouncer

Kawka,

Vennes,

Ferrario

et al. 2021

Preprint

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We report the discovery of a rare close binary system, SMSS J160639.78-100010.7, comprised of a magnetic white dwarf with a field of about 30 MG and a brown dwarf. We measured an orbital period of 92 min which is consistent with the photometric period. Minimum and maximum light occur at the orbital quadratures Φ = 0.25 and 0.75, respectively, and cannot be caused by reflection on the brown dwarf, but, instead, by a spot on the synchronously rotating magnetic white dwarf. The brown dwarf does not fill its Roche lobe and the system may be in a low-accretion state or, more likely, in a detached state following episodes of mass transfer. SMSS J160639.78-100010.7 is the nearest known magnetic white dwarf plus brown dwarf system.

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“…Previously, ∼10 WDs accreting from brown dwarfs have been reported (Longstaff et al 2019). Only two of them show X-ray emission, EF Eridani (Schwope et al 2007) and SDSSJ121209.31+013627.7 (Stelzer et al 2017); however, both are cool WDs with effective temperatures lower than 10,000 K, and both are polars whose strong magnetic fields channel material from the companion to the WDs' magnetic poles to be accreted. The three WDs with hard X-ray emission reported in this paper have much higher effective temperatures than these polars.…”

Section: Accretion From a Hidden Companionmentioning

confidence: 99%

Hard X-ray Emission Associated with White Dwarfs. IV. Signs of Accretion from Sub-stellar Companions

Chu,

Toala,

Guerrero

et al. 2021

Preprint

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KPD 0005+5106, with an effective temperature of ≃200,000 K, is one of the hottest white dwarfs (WDs). ROSAT unexpectedly detected "hard" (∼1 keV) X-rays from this apparently single WD. We have obtained Chandra observations that confirm the spatial coincidence of this hard X-ray source with KPD 0005+5106. We have also obtained XMM-Newton observations of KPD 0005+5106, as well as PG 1159−035 and WD 0121−756, which are also apparently single and whose hard X-rays were detected by ROSAT at 3σ-4σ levels. The XMM-Newton spectra of the three WDs show remarkably similar shapes that can be fitted by models including a blackbody component for the stellar photospheric emission, a thermal plasma emission component, and a power-law component. Their X-ray luminosities in the 0.6 − 3.0 keV band range from 4 × 10 29 to 4 × 10 30 erg s −1 . The XMM-Newton EPIC-pn softband (0.3 − 0.5 keV) lightcurve of KPD 0005+5106 is essentially constant, but the hard-band (0.6 − 3.0 keV) lightcurve shows periodic variations. An analysis of the generalized Lomb-Scargle periodograms for the XMM-Newton and Chandra hard-band lightcurves finds a convincing modulation (false alarm probability of 0.41%) with a period of 4.7±0.3 hr. Assuming that this period corresponds to a binary orbital period, the Roche radii of three viable types of companion have been calculated: M9V star, T brown dwarf, and Jupiter-like planet. Only the planet has a size larger than its Roche radius, although the M9V star and T brown dwarf may be heated by the WD and inflate past the Roche radius. Thus, all three types of companion may be donors to fuel accretion-powered hard X-ray emission.

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X-ray orbital modulation of a white dwarf accreting from an L dwarf

Cited by 22 publications

References 33 publications

Magnetic white dwarfs in post-common-envelope binaries

Magnetic white dwarfs in post-common-envelope binaries

The magnetic system SMSS J1606-1000 as a period bouncer

Hard X-ray Emission Associated with White Dwarfs. IV. Signs of Accretion from Sub-stellar Companions

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