polluted white dwarfs & compositions of extrasolar minor planets · 2019. 5. 19. · white...

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

sxu@gemini.edu