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Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems
UCL, Dept Phys & Astron, London WC1E 6BT, England..
Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England..
Columbia Univ, Dept Phys, 538 W 120th St, New York, NY 10027 USA..
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 474, no 1, p. 947-960Article in journal (Refereed) Published
Abstract [en]

This paper reports circular spectropolarimetry and X-ray observations of several polluted white dwarfs including WD 1145+017, with the aim to constrain the behaviour of disc material and instantaneous accretion rates in these evolved planetary systems. Two stars with previously observed Zeeman splitting, WD 0322-019 and WD 2105-820, are detected above 5 sigma and < B-z > > 1 kG, while WD 1145+017, WD 1929+011, and WD 2326+049 yield (null) detections below this minimum level of confidence. For these latter three stars, high-resolution spectra and atmospheric modelling are used to obtain limits on magnetic field strengths via the absence of Zeeman splitting, finding B-* < 20 kG based on data with resolving power R approximate to 40 000. An analytical framework is presented for bulk Earth composition material falling on to the magnetic polar regions of white dwarfs, where X-rays and cyclotron radiation may contribute to accretion luminosity. This analysis is applied to X-ray data for WD 1145+017, WD 1729+371, and WD 2326+049, and the upper bound count rates are modelled with spectra for a range of plasma kT = 1-10 keV in both the magnetic and non-magnetic accretion regimes. The results for all three stars are consistent with a typical dusty white dwarf in a steady state at 108-109 g s(-1). In particular, the non-magnetic limits for WD 1145+017 are found to be well below previous estimates of up to 10(12) g s(-1), and likely below 1010 g s(-1), thus suggesting the star-disc system may be average in its evolutionary state, and only special in viewing geometry.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS , 2018. Vol. 474, no 1, p. 947-960
Keywords [en]
circumstellar matter, stars: magnetic field, planetary systems, white dwarfs, X-rays: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-348400DOI: 10.1093/mnras/stx2664ISI: 000424339500070OAI: oai:DiVA.org:uu-348400DiVA, id: diva2:1197381
Available from: 2018-04-12 Created: 2018-04-12 Last updated: 2018-04-12Bibliographically approved

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Kochukhov, Oleg

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