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SUMMARY:Polluted White Dwarfs: Constraints on the Origin and Geology of Ex
 oplanetary Material - John Harrison (Cambridge)
DTSTART:20180215T113000Z
DTEND:20180215T123000Z
UID:TALK98098@talks.cam.ac.uk
CONTACT:Ed Gillen
DESCRIPTION:White dwarfs that have accreted rocky planetary bodies provide
  unique insights regarding the bulk composition of exoplanetary material. 
 The frequency of solar system-like chemistry and geology in the galaxy is 
 poorly understood. In our work we use the observed pollutant chemical abun
 dances to constrain where in the planetary system the pollutant bodies ori
 ginated and their geological and collisional history. We find that at leas
 t 2\, but possibly up to 12\, of the 17 systems analysed in our work have 
 accreted a body dominated by either a core-like or a mantle-like material.
  These bodies are expected to be fragments formed in collisions between la
 rger bodies that have differentiated into a core and a mantle\, providing 
 evidence for differentiation in exosystems. The even spread in the core ma
 ss fraction of the pollutants\, and the lack of crust-rich pollutants in t
 he 17 systems studied here agree with such a collisional model. The compos
 itions of many pollutants exhibit trends related to elemental volatility\,
  which we link to the temperatures and\, thus\, the locations at which the
 se bodies formed. Our analysis shows that the abundances observed in 13 of
  the 17 systems considered are consistent with the compositions of nearby 
 stars in combination with a trend related to volatility. The even spread a
 nd large range in the predicted formation location of the pollutants sugge
 sts that pollutants arrive in white dwarf atmospheres with a roughly equal
  efficiency from a wide range of radial locations\, from very close to the
  host star\, where refractory species dominate\, to outside of the nitroge
 n ice line\, where many ice species are abundant. 
LOCATION:Martin Ryle Seminar Room\, Kavli Institute
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