Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 451, Issue 3, Pages 3237-3248Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv1201
Keywords
planets and satellites: composition; stars: individual: SDSS J0845+2257; planetary systems; white dwarfs
Categories
Funding
- European Research Council under the European Union [320964]
- FONDECYT [3140585]
- NASA [NAS 5-26555]
- Alfred P. Sloan Foundation
- National Science Foundation
- US Department of Energy Office of Science
- Gemini South Telescope [GS-2010A-Q-17]
- ESO VLT at the La Silla Paranal Observatory [081.C-0466(A), 082.C-0495(A), 383.C-0695(A), 386.C-0218(B), 094.D-0344(A)]
- [11561]
- STFC [ST/L000733/1, ST/M006492/1] Funding Source: UKRI
- Cancer Research UK [11561] Funding Source: researchfish
- Science and Technology Facilities Council [ST/M006492/1, ST/L000733/1] Funding Source: researchfish
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We present a detailed study of the metal-polluted DB white dwarf SDSS J0845+2257 (Ton 345). Using high-resolution Hubble Space Telescope/Cosmic Origins Spectrograph and Very Large Telescope spectroscopy, we have detected hydrogen and 11 metals in the atmosphere of the white dwarf. The origin of these metals is almost certainly the circumstellar disc of dusty and gaseous debris from a tidally disrupted planetesimal, accreting at a rate of 1.6 x 10(10) g s(-1). Studying the chemical abundances of the accreted material demonstrates that the planetesimal had a composition similar to the Earth, dominated by rocky silicates and metallic iron, with a low water content. The mass of metals within the convection zone of the white dwarf corresponds to an asteroid of at least similar to 130-170 km in diameter, although the presence of ongoing accretion from the debris disc implies that the planetesimal was probably larger than this. While a previous abundance study of the accreted material has shown an anomalously high mass fraction of carbon (15 per cent) compared to the bulk Earth, our independent analysis results in a carbon abundance of just 2.5 per cent. Enhanced abundances of core material (Fe, Ni) suggest that the accreted object may have lost a portion of its mantle, possibly due to stellar wind stripping in the asymptotic giant branch. Time series spectroscopy reveals variable emission from the orbiting gaseous disc, demonstrating that the evolved planetary system at SDSS J0845+2257 is dynamically active.
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