10 September 2014

Siyi XuESO Fellow (Garching)

Elemental Compositions of Extrasolar Planetesimals

10 September 2014

Thanks to all my collaborators…

Michael Jura Ben Zuckerman Beth Klein Detlev Koester

(Poster DD-2)

(i) Nebular Condensation

* 94% O, Fe, Si, Mg

* 0.17-0.39% C

(ii) Differentiation

Is Earth normal?

Earth as we know…

Fe

Si, Mg

Mg

Wesemael+1993

Typical white dwarf spectra:

Evidence I: 25-50% WDs show heavy elements in the atmospheres.

There must be some external source constantly feeding the WDs!

Gaensicke, Koester+2012

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

Xu+ 2013

PG 1225-079

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

Core/Crust

Differentiation and collision is common among extrasolar planetesimals

log n(Fe)/n(Si)

log

n(M

g)/

n(S

i)

Jura & Young 2014

A pilot search for extrasolar plate tectonics

• Earth’s continental crust is enriched in incompatible elements, e.g. Ba, Sr..

Jura+ 2014

less than 1% material is from continental crust

GD 362

• 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!

Summary

sxu@eso.org

Back Up Slides

GD 362: the best match solar system analog is mesosiderite

Condensation Temperature

volatile refractory