A white dwarf accreting planetary material determined from X-ray observations

Tim Cunningham (), Peter J. Wheatley, Pier-Emmanuel Tremblay, Boris T. Gänsicke, George W. King, Odette Toloza and Dimitri Veras
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Tim Cunningham: The University of Warwick
Peter J. Wheatley: The University of Warwick
Pier-Emmanuel Tremblay: The University of Warwick
Boris T. Gänsicke: The University of Warwick
George W. King: University of Michigan
Odette Toloza: Universidad Técnica Federico Santa María
Dimitri Veras: The University of Warwick

Nature, 2022, vol. 602, issue 7896, 219-222

Abstract: Abstract The atmospheres of a large proportion of white dwarf stars are polluted by heavy elements1 that are expected to sink out of visible layers on short timescales2,3. This has been interpreted as a signature of ongoing accretion of debris from asteroids4, comets5 and giant planets6. This scenario is supported by the detection of debris discs7 and transits of planetary fragments8 around some white dwarfs. However, photospheric metals are only indirect evidence for ongoing accretion, and the inferred accretion rates and parent body compositions heavily depend on models of diffusion and mixing processes within the white dwarf atmosphere9–11. Here we report a 4.4σ detection of X-rays from a polluted white dwarf, G29–38. From the measured X-ray luminosity, we derive an instantaneous accretion rate of $${\dot{M}}_{{\rm{X}}}={1.63}_{-0.40}^{+1.29}\times {10}^{9}\,{\rm{g}}\,{{\rm{s}}}^{-1}$$ M ̇ X = 1.63 − 0.40 + 1.29 × 10 9 g s − 1 , which is independent of stellar atmosphere models. This rate is higher than estimates from past studies of the photospheric abundances of G29–38, suggesting that convective overshoot may be needed to model the spectra of debris-accreting white dwarfs. We measure a low plasma temperature of kBT = 0.5 ± 0.2 keV, corroborating the predicted bombardment solution for white dwarfs accreting at low accretion rates12,13.

Date: 2022
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DOI: 10.1038/s41586-021-04300-w

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