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SUMMARY:Chemistry and evolution of the oldest white dwarf planetary system
 s - Mark Hollands (Warwick)
DTSTART:20161102T160000Z
DTEND:20161102T170000Z
UID:TALK67928@talks.cam.ac.uk
CONTACT:Ed Gillen
DESCRIPTION:Almost all main-sequence stars\, including the Sun\, will even
 tually become white dwarfs.\nDuring the giant-stages of the stellar evolut
 ion\, planetary objects within about 1 AU will be engulfed\,\nwhile those 
 further out will survive to the white dwarf stage.\nRocky-planetesimals (i
 .e. asteroids/minor planets) that are accreted onto the central degenerate
 -star\,\nlead to white dwarf atmospheres enriched with metals\, rather tha
 n the pure hydrogen/helium\ncomposition expected from gravitational settli
 ng of elements.\nThe spectra of these "metal-polluted" white dwarfs theref
 ore provide a unique tool\nfor analysing the bulk compositions of rocky ma
 terial outside of the Solar-system.\n\nUsing SDSS spectra\, we have identi
 fied 231 white dwarfs that are both old (cooling ages 1--8 Gyr)\,\nand hav
 e atmospheres rich in metallic elements. Abundance analyses of the spectra
 \nreveal wide ranging compositions from crust-like to core-like\,\nwith th
 e most extreme cases indicating highly differentiated planetesimals.\nAddi
 tionally\, the old ages of the systems we identify have allowed us to prob
 e\nremnant planetary system evolution.\nWe find compelling evidence that w
 hite dwarfs deplete their planetesimal reservoirs on a\n~1 Gyr e-folding t
 imescale\, an effect not seen in other studies which have predominantly\nf
 ocussed on much younger white dwarfs.
LOCATION:Martin Ryle Seminar Room\, Kavli Institute
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