Magnetism, X-rays and accretion rates in WD1145+017 and other polluted white dwarf systems

J. Farihi, L. Fossati, P. J. Wheatley, B. D. Metzger, J. Mauerhan, S. Bachman, B. T. Gänsicke, S. Redfield, P. W. Cauley, O. Kochukhov, N. Achilleos, N. Stone

Research output: Contribution to journalArticlepeer-review


This paper reports circular spectropolarimetry and X-ray observations of several polluted white dwarfs including WD1145+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, WD0322-019 and WD2105-820, are detected above 5s and 〈Bz〉> 1 kG, while WD1145+017, WD1929+011, and WD2326+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 ≈ 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 WD1145+017, WD1729+371, and WD2326+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 WD1145+017 are found to be well below previous estimates of up to 1012 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.

Original languageEnglish
Pages (from-to)947-960
Number of pages14
Issue number1
StatePublished - Feb 2018
Externally publishedYes


  • Circumstellar matter
  • Planetary systems
  • Stars: magnetic field
  • White dwarfs
  • X-rays: stars

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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