Transcript Elemental Compositions of Extrasolar Planetesimals

Elemental Compositions of
Extrasolar Planetesimals
Siyi Xu
ESO Fellow (Garching)
10 September 2014
Thanks to all my collaborators…
Michael Jura
Ben Zuckerman
Beth Klein
Detlev Koester
(Poster DD-2)
10 September 2014
Earth as we know…
(i) Nebular
Condensation
* 94% O, Fe, Si, Mg
* 0.17-0.39% C
(ii) Differentiation
Mg
Fe
Is Earth normal?
Si, Mg
Typical white dwarf spectra:
Wesemael+1993
Evidence I: 25-50% WDs show
heavy elements in the atmospheres.
Gaensicke, Koester+2012
There must be some external source
constantly feeding the WDs!
Evidence II: ~4% single WDs show infrared
excess from an orbiting dust disk.
High-resolution spectroscopic studies of
heavy-element-enriched white dwarfs uniquely
measure the bulk compositions of
extrasolar planetesimals.
Keck/HIRES Spectra
Xu+ 2014
HST/COS Spectra
PG 1225-079
Xu+ 2013
Planetesimals Accreted onto WDs:
• mass 1018-1023g
• 19 heavy elements detected C, S, O, Na,
Cu, Mn, P, Cr, Si, Mg, Fe, Co, Ni, V, Sr,
Ca, Ti, Al, Sc
The compositions of extrasolar
planetesimals resemble bulk earth.
Xu+ 2014
log n(Mg)/n(Si)
Differentiation and collision is common
among extrasolar planetesimals
log n(Fe)/n(Si)
Core/Crust
Jura & Young 2014
A pilot search for extrasolar plate tectonics
• Earth’s continental crust is enriched in
incompatible elements, e.g. Ba, Sr..
less than 1% material is from
continental crust
GD 362
Jura+ 2014
Summary
• Heavy-element-enriched WDs are a powerful tool to
study compositions of extrasolar planetesimals
• Extrasolar planetesimals resemble bulk Earth
– Dominated by O ,Mg, Si, Fe, very little C
– Differentiation and collision is widespread
Thank you!
[email protected]
Back Up Slides
GD 362: the best match solar system
analog is mesosiderite
volatile
refractory
Condensation Temperature