Where Are the Magnetic White Dwarfs with Detached, Nondegenerate Companions?

Liebert, James; Wickramsinghe, Dayal T.; Schmidt, Gary D.; Silvestri, Nicole M.; Hawley, Suzanne L.; Szkody, Paula; Ferrario, Lilia; Webbink, R. F.; Oswalt, Terry D.; Smith, J. Allyn; Lemagie, Mara P.

doi:10.1086/429639

Cited by 91 publications

(117 citation statements)

References 47 publications

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“…We here draw attention to the fact that there is no indication for any strong magnetic white dwarf primary in the systems of our sample (and they appear to be pretty rare in pre-CVs in general; Liebert et al 2005;Silvestri et al 2007). These objects therefore will eventually evolve into non-magnetic CVs without anomalous abundances.…”

Section: Discussionmentioning

confidence: 77%

K-band spectroscopy of pre-cataclysmic variables

Tappert

Gänsicke

Schmidtobreick

et al. 2007

A&A

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Aims. There exists now substantial evidence for abundance anomalies in a number of cataclysmic variables (CVs), indicating that the photosphere of the secondary star incorporates thermonuclear processed material. However, the spectral energy distribution in CVs is usually dominated by the radiation produced by the accretion process, severely hindering an investigation of the stellar components. On the other hand, depending on how the secondary star has acquired such material, the above mentioned abundance anomalies could also be present in pre-CVs, i.e. detached white/red dwarf binaries that will eventually evolve into CVs, but have not yet started mass transfer, and therefore allow for an unobstructed view on the secondary star at infrared wavelengths. Methods. We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to examine them for anomalous chemical abundances. In particular, we study the strength of the 12 CO and 13 CO absorption bands that have been found diminished and enhanced, respectively, in similar studies of CVs.Results. All our systems show CO abundances that are within the range observed for single stars. The weakest 12 CO bands with respect to the spectral type are found in the pre-CV BPM 71214, although on a much smaller scale than observed in CVs. Furthermore there is no evidence for enhanced 13 CO. Taking into account that our sample is subject to the present observational bias that favours the discovery of young pre-CVs with secondary stars of late spectral types, we can conclude the following: 1) our study provides observational proof that the CO anomalies discovered in certain CVs are not due to any material acquired during the common envelope phase, and 2) if the CO anomalies in certain CVs are not due to accretion of processed material during nova outburst, then the progenitors of these CVs are of a significantly different type than the currently known sample of pre-CVs.

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Section: Discussionmentioning

confidence: 77%

K-band spectroscopy of pre-cataclysmic variables

Tappert

Gänsicke

Schmidtobreick

et al. 2007

A&A

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“…Liebert et al (2005) noted the absence of non-accreting magnetic white dwarfs (MWDs) among the more than 1200 WDMS binaries compiled by Silvestri et al (2007) and various other samples (Marsh 2000;Ritter & Kolb 2003;Schreiber & Gänsicke 2003;Morales-Rueda et al 2005;Shimansky et al 2006). MWDs are clearly underrepresented in current WDMS samples compared to the ∼10% fraction in the field (Liebert et al 2003).…”

Section: Discussionmentioning

confidence: 99%

“…MWDs are clearly underrepresented in current WDMS samples compared to the ∼10% fraction in the field (Liebert et al 2003). As a first possible solution to this fact, Liebert et al (2005) suggested that, analogous to single magnetic white dwarfs, the magnetic white dwarfs in WDMS binaries are more massive, and therefore smaller and less luminous compared to those in non-magnetic WDMS binaries which could result in an observational bias against their detection. However, Silvestri et al (2007) convincingly demonstrate that such systems would be easily identified, if they were present in the SDSS data base.…”

Section: Discussionmentioning

confidence: 99%

Post common envelope binaries from the SDSS

Schwope¹,

Gómez‐Morán²,

Schreiber

et al. 2009

A&A

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We report the discovery of the ninth pre-polar consisting of a late-type ZAMS secondary and a magnetic white dwarf. The white dwarf accretes at an extreme low rate,Ṁ ∼ 10 −14 M yr −1 , from the wind of the companion donor star. The source was found in our systematic search for WD/MS binaries within SDSS/SEGUE. Based on seven Sloan spectra we estimate a binary period of ∼200, 230, or 270 min. The UV to IR spectral energy distribution was decomposed into a dM3-dM4 ZAMS secondary and a cool white dwarf, ∼9000 K, which consistently imply a distance between 360 and 420 pc. The optical spectrum displays one pronounced cyclotron hump, likely originating from a low-temperature plasma, ∼1 keV, in a field of 108 MG. We comment on the evolutionary link between polars and pre-polars.

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“…Remarkably, not a single observed close, detached binary system (in which the primary is a WD and the companion is a low-mass main-sequence star) contains a HFMWD (11)(12)(13). If the magnetic field strengths of white dwarfs were independent of binary interactions, then the observed distribution of isolated WDs should be similar to those in detached binaries.…”

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confidence: 99%

Formation of high-field magnetic white dwarfs from common envelopes

Nordhaus

Wellons

Spiegel

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

119

116

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The origin of highly magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, such as a planet, brown dwarf, or low-mass star, is engulfed by a post-mainsequence giant, gravitational torques in the envelope of the giant lead to a reduction of the companion's orbit. Sufficiently low-mass companions in-spiral until they are shredded by the strong gravitational tides near the white dwarf core. Subsequent formation of a super-Eddington accretion disk from the disrupted companion inside a common envelope can dramatically amplify magnetic fields via a dynamo. Here, we show that these disk-generated fields are sufficiently strong to explain the observed range of magnetic field strengths for isolated, high-field magnetic white dwarfs. A higher-mass binary analogue may also contribute to the origin of magnetar fields.magnetohydrodynamics | compact objects

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Where Are the Magnetic White Dwarfs with Detached, Nondegenerate Companions?

Cited by 91 publications

References 47 publications

K-band spectroscopy of pre-cataclysmic variables

K-band spectroscopy of pre-cataclysmic variables

Post common envelope binaries from the SDSS

Formation of high-field magnetic white dwarfs from common envelopes

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