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Polluted White Dwarfs & Compositions of Extrasolar
Minor PlanetsSiyi Xu (许偲艺)
Assistant AstronomerGemini Observatory/AURA
2019-05-15ExoComets
White Dwarfs: A Common End of Stellar Evolution
Stratified Atmosphere
Solar System
White Dwarf
H/He AtomHeavy Atom
10-3 AU
RocheLimit
DustSublimation
Giant Planet
10 AU
A Schematic Illustrations
0 planets L
~10 gas disks
1 asteroid
~40 dust disks
~100s Polluted WDs
1018 – 1023 g106 – 1011 g/s
Chemical Composition of the Disintegrating Body
(1 system)
WD 1145+017: Phase-Folded Light Curves Show Rapid Evolution
Gary+ 2017
2015
2016
Xu+ in press
• Multi-wavelength Observations: UV to 4.5 µm• Transit depths are the same• If dust cloud is optically thin, a dearth of small particles
Transiting Exoplanet Survey Satellite (TESS)
Chemical Composition of the Dust Disk(~40 systems)
Spitzer/IRS observations of G29-38Em
issiv
ity =
Obs
erve
d / Bν(
930
K)
Wavelength (μm)
am. carbon
carbonatesPAHwater vap.
water ice
sulfidesphyllosilicates
cryst. pyr.
am. silicates
cryst. forsterite
5 10 30 3515 20 25
0.0
0.5
1.0
Reach+ 2009
Amorphous CSilicatesWater Ice
Metal sulfides
IRS observations of other dusty WDs
Farihi+ 2016
Chemical Composition of the Gas Disk(~10 systems)
Gas Debris around WDs
Gaensicke+ 2006
Puzzles:• Why?• Where?• How?• Eccentricity?
WD 1226+110: Ca IR Triplet
WD 1145+017: absorption from CS gas
Xu+ 2016, in pressVelocity (km/s)
Nor
mal
ized
Flu
x
Velocity (km/s)
Chemical Composition of the Polluted Atmosphere
(~100s systems)1018 – 1023 g106 – 1011 g/s
High-resolution Spectroscopy of WD 1145+017
UVC, N, S, O, Mg, Al, Si, P, Mn, Fe, Ni
OpticalNa, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Sr
Xu+ in press
Abundance Analysis of Polluted WDs
Dufour+ 2012
Photometry, parallax, low-res spectra à temperature & log g
à Abundances
Compositions of Extrasolar Minor Planets
10000 12000 14000 16000 18000 20000 22000 24000
Bulk Earth
Comet Halley
Temperature (K)
Xu+ 2017
Comet Halley AnalogWD 1425+540
Accretion of KBO Analog onto WDs
• WD 1425+540 has a K dwarf companion
• KBO analog originally located ~120 AU
• Galactic tide? Kozai-Lidov Mechanism?
From SDSS
40arcsec(2240AU)
White Dwarf
H/He AtomHeavy Atom
10-3 AU
RocheLimit
DustSublimation
Giant Planet
10 AU
0 planets L
~10 gas disks
1 asteroid
~40 dust disks
~100s Polluted WDs
1018 – 1023 g106 – 1011 g/s
Material Transfer: the disintegrating asteroid à dust & gas disk à atmosphere
G29-38: Abundance Comparison
Dust Disk
WD Atmosphere
Xu+ 2014
Two postdoc openings per year!
White Dwarf
H/He AtomHeavy Atom
10-3 AU
RocheLimit
DustSublimation
Giant Planet
10 AU
Many opportunities to study compositions with WD planetary systems!
0 planets L
~10 gas disks
1 asteroid
~40 dust disks
~100s Polluted WDs
1018 – 1023 g106 – 1011 g/s
