Polluted White Dwarfs: Constraints on the Origin and Geology of Exoplanetary Material
Monthly Notices of the Royal Astronomical Society
Oxford University Press
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Bonsor-Matthews, A., Harrison, J., & Nikku, M. (2018). Polluted White Dwarfs: Constraints on the Origin and Geology of Exoplanetary Material. Monthly Notices of the Royal Astronomical Society, 479 (3), 3814-3841. https://doi.org/10.1093/mnras/sty1700
White dwarfs that have accreted rocky planetary bodies provide unique insights regarding the bulk composition of exoplanetary material. The analysis presented here uses observed pollutant abundances to constrain both where in the planetary system the pollutant bodies originated, and the geological and collisional history of the pollutant bodies. At least 1, but possibly up to 9, of the 17 systems analysed have accreted a body dominated by either core- like or mantle-like material. The approximately even spread in the core mass fraction of the pollutants and the lack of crust-rich pollutants in the 17 systems studied here suggest that the pollutants are often the fragments produced by the collision of larger differentiated bodies. The compositions of many pollutants exhibit trends related to elemental volatility, which we link to the temperatures and, thus, the locations at which these bodies formed. Our analysis found that the abundances observed in 11 of the 17 systems considered are consistent with the compositions of nearby stars in combination with a trend related to elemental volatility. The even spread and large range in the predicted formation location of the pollutants suggests that pollutants arrive in white dwarf atmospheres with a roughly equal efficiency from a wide range of radial locations. Ratios of elements with different condensation temperatures such as Ca/Mg, Na/Mg, and O/Mg distinguish between different formation temperatures, whilst pairs of ratios of siderophilic and lithophilic elements such as Fe/Mg, Ni/Mg and Al/Mg, Ca/Mg distinguish between temperature dependent trends and geological trends.
white dwarfs, stars: abundances, planets and satellites: composition, formation, minor planets, asteroids: general, protoplanetary discs
We are grateful to the Science & Technology Facilities Council, and the Royal Society - Dorothy Hodgkin Fellowship for funding the authors of this paper.
Royal Society (DH150088)
Science and Technology Facilities Council (ST/N000927/1)
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External DOI: https://doi.org/10.1093/mnras/sty1700
This record's URL: https://www.repository.cam.ac.uk/handle/1810/282905