dusty debris disks exoplanets - victoria centre · 10.10.2007  · 1 dusty debris disks &...

Post on 29-Sep-2020

1 Views

Category:

Documents

0 Downloads

Preview:

Click to see full reader

TRANSCRIPT

1

DUSTY DEBRIS DISKS&

EXOPLANETS

DUSTY DEBRIS DISKS&

EXOPLANETS

James R. Graham

University of California, Berkeley

October 10, 2007

2

Introduction

Debris Disks

&

Planets

3

HOW TO DETECT PLANETS

• Voyager spacecraft “family portrait” of the solar system» Solar system observations are the initial data point for the theory of

planet formation

» Virtually all we know about exoplanets comes from indirectDoppler methods that yield three numbers: M sin i, a & e

4

EXTRA SOLAR PLANETS

• Indirect methods havefound over 200exoplanets

• Is our solar systemtypical?

• How do planets form?

» “Bottom up” or “topdown”?

• Debris disks holdclues to planets & theirformation

Doppler Planets

5

OBSERVATION OF A DEBRIS DISKOBSERVATION OF A DEBRIS DISK

6

THE VISIBLE SKY (Galactic Coords)

Axel Mellinger, 2000

7

THE INFRARED SKY (8–200 !m)

8Leinert & Gruen 1990

EMISSION FROM SOLAR ZODIACAL DUST

T ! 250 KT ! 6000 K

0.1 0.5 1.0 5 10 50 100

Wavelength (!m)

9

THE “VEGA PHENOMENON”: YOUNG MAINSEQUENCE STARS WITH IR EMISSION

THE “VEGA PHENOMENON”: YOUNG MAINSEQUENCE STARS WITH IR EMISSION

Backman & Paresce 1993 PP III"The Big Three"

Fomalhaut ! Pic

Wavelength (!m)

“Discovery of a shell around Alpha Lyrae”H. H. Aumann et al. 1984, ApJL 278 23

Vega

10

THE ! PIC DEBRIS DISKTHE ! PIC DEBRIS DISK

Smith & Terrile 1984

Visible light traces starlight scattered by dust

11

REPLENISHED DUST DISKSREPLENISHED DUST DISKS

• ! Pic: ~ 10 Myr• Zodiacal dust: 4.55 Gyr

Kalas & Jewitt 1995

Destruction of larger bodies supply fresh dust

12

THE ! PIC DEBRIS DISKTHE ! PIC DEBRIS DISK

Smith & Terrile 1984

Visible light traces starlight scattered by dust

13

THE SOLAR KUIPER BELT

SKBO

Plutinos

KBO

14

THE SOLAR KUIPER BELT

Art by Don Dixon (2000)

STScI May Symposium, 2005 Malhotra

15

THE ! PIC DEBRIS DISKTHE ! PIC DEBRIS DISK

Smith & Terrile 1984

Visible light traces starlight scattered by dust

16

PLANETS SCULPT THE SOLAR SYSTEM

• Jupiter shepherdsthe asteroids» Stable orbits

between Marsand Jupiter

» Trojan asteroids

Jupiter

17Robert H. McNaught

18

19

SCULPTING KUIPER BELT DUST

• Pioneer 11 detected constant dust

density between 30-50 AU

• Kuiper Belt produces !m to mm

sized dust equivalent to one km-

sized comet ground up every year

» Tiny (< 0.5!m) particles are blown

out by radiation pressure

» Bound grains spiral inward by

Poynting-Robertson drag

» Temporary trapping in Neptune’s

mean motion resonances

produces azimuthal structure

» Gravitational scattering by Jupiter

& Saturn ejects most particles;

tiny fraction of KB dust enters the

inner solar systemMoro-Martin & Malhotra, 2003

STScI May Symposium, 2005 Malhotra

AU

20

LESSONS FOR DUSTY DEBRIS DISKS

• Planets within debris disks sculpt the dust

distribution

With solar

system planetsWithout planets

Minimum at Neptune’s

position (to avoid resonant

planet)

Ring-like structure along

Neptune’s orbit

(trapping into mean

motion resonances)

Clearing of dust < 10 AU

(gravitational scattering

by Jupiter & Saturn)100 AU

21

Fomalhaut

Probing Debris Disk Structure for

Signs of Planets

22

!! PICTORIS IN PICTORIS IN SCATTEREDSCATTERED LIGHTLIGHT

23

SUB-MILLIMETER TELESCOPES ON

MAUNA KEA

24

The Fanatastic Four at 850 !m

20 pc20 pc 7.7 pc7.7 pc 7.7 pc7.7 pc 3.2 pc3.2 pc

JCMT/SCUBA maps of debris disk stars show intriguing structure at

sub-millimeter wavelengths—the resolution is poorHolland et al. 1998;

Greaves et al. 1998

25S

26

FOMALHAUT IN CONTEXTFOMALHAUT IN CONTEXT

• Spectral type A3V

• Young & nearby

(8 pc)

• At 200-300 Myr it

may be entering

“late heavy

bombardment”

phase recorded in

the Solar System

cratering history

27

SEARCHING FOR DEBRIS DISKS WITHSEARCHING FOR DEBRIS DISKS WITH

THE HUBBLE SPACE TELESCOPETHE HUBBLE SPACE TELESCOPE

• In March 2002 Hubblewas upgraded with anew camera» Advanced Camera for

Surveys (ACS)

» Coronagraphic mode ofoperation with occultingspots to block the light ofbright stars

• New opportunity toimage these elusivedebris disks at highresolution

28

FOMALHAUTFOMALHAUT’’s s DISK DISCOVEREDDISK DISCOVERED

• Even with the ACS

coronagraph

blocking most of

the stellar light a

faint disk isundetectable

» Search by

subtracting an

image of Vega from

that of Fomalhaut

29

Discovery

image, May 17,

2004, F814W

JCMT SCUBA

450 micron

map (Wyatt &

Dent 2002)

HST FOMALHAUT IMAGE & SUB-MM DATAHST FOMALHAUT IMAGE & SUB-MM DATA

30

FOMALHAUT F814W + F606WFOMALHAUT F814W + F606W

25 mas /

pix,

FWHM =

60 mas =

0.5 AU

Kalas, Graham & Clampin 2005, Nature, June 2005

31

BELT PARAMETERSBELT PARAMETERS

• Semimajor axis: 140.7± 1.8 AU

• Semiminor axis: 57.5 ± 0.7 AU

• PA major axis: 156.0˚±0.3˚

• Inclination: 65.9˚± 0.4˚

• Projected offset: 13.4 ± 1 AU

• PA of offset: 156.0˚ ± 0.3˚

• Deprojected offset: 15.3 AU

• Eccentricity: 0.11±0.04

Orbital period at 140 AU = 1200 yr

32

DUST BELT SIMULATIONS

• Adam Deller &

Sarah

Maddison,

(Swinburne U.)

• 2 MJ planet

• e = 0.3

• a = 70 AU (420

yr)

33

DUST BELT SIMULATIONS

• Adam Deller &

Sarah

Maddison,

(Swinburne)

• 2 MJ planet

• e = 0.3

• a = 70 AU (420

yr)

34

Beta Pic’s Sibling:

AU Microscopii

What are Debris Disks Made of?

35

AU Microscopii (GJ 803)• High proper motion M1Ve

flare star GJ 803

» 9.9 pc

• Discovered in the IRAS PSCwith a 60 !m excess(Tsikoudi 1988; Mathioudakis& Doyle 1991)

• Member of the ! Pic movinggroup (Barrado y Navascues1999)

» Young (12+8-4 Myr)

15 13 11 9

log("/Hz)

Kala

s &

Delto

rn (1

999)

Math

ioudakis

& D

oyle

1991

Zuckerm

an, S

ong, e

t al. 2

001

36

Discovery of the Scattered Light Disk

UH 2.2-m, R-band, 900 s, seeing = 1.1"

Kala

s, L

iu, &

Matth

ew

s2004

37

88-inch Telescope & CoronagraphZ

uckerm

an, G

radie

, et a

l. (UC

LA

/Haw

aii)

38

! Pic & AU Mic

39

F606W

40

AU Mic in Polarized Light

• Two orbits Hubble/Advanced Camera in visible light» 1.’’8 Ø coronagraph spot

» Combined data from three polarizing filters at 0°, 60°, & 120°

• False color encodes brightness of scattered starlight» Ticks show orientation and strength of polarization

• To produce such high polarization the grains must befluffy or porous

1 arc sec

10 AU

Graham et al. 2007

41

Porous Low Index Materials

Aerogel

• Terrestrial examplesof porous materialsare snow and aerogel» The porosity is often a

clue to how thematerial formed

» e.g., compare snowflakes (97% emptyspace; 3% ice) withhail stones (mostlysolid ice)

Dry champagne powder

42

AU Mic Cartoon

43

Scattering, Refraction & Polarization

• HST measures how dustgrains in orbit around AUMic scatter starlight» Reflection & refraction of light

are quantified by the refractiveindex

• When light is reflected it isselectively polarized

» Degree of polarization dependson the angles & the refractiveindex

» e.g., on a clear day skylight isstrongly polarized as is sunlightreflected off the ocean or snow

• The refractive indexdepends on the density &very low values meanporous or fluffy material

44

Porous Grains

• Porous grains are anatural consequence ofvarious grain growthscenarios» Diffusion limited

aggregation

» Cluster-clusteraggregation

» Self avoiding random walk

Wrig

ht 1

987

• Porosity is a clue to the formation mechanism &processing history» Snow flakes vs. hailstones

45

ACS

March 2002–January 2007

46

Life After Hubble

Ground Base Telescopes &

Adaptive Optics

47

Why is AO Needed?

Natural seeing AO corrected

48

Why is AO

Needed?• Refractive index

variations in the

atmosphere distort

incoming wavefronts

» Swimming pool

analogy

49

How to Measure Wavefront Errors

Shack-Hartmann wavefront sensor

50

How a Deformable Mirror Works: I

BEFORE AFTER

Incoming

Wave with

Aberration

Deformable

MirrorCorrected

Wavefront

How a Deformable Mirror Works: II

52

Mt Hamilton

Feb 2001120-inch

Telescope

53

AO bench

120-inch

Telescope

54

Lick/LLNL Laser

Guide Star

• Pulsed dye laser

» Nd:YAG pump

» 100 ns pulse/11 kHz

rep rate

» 11-12 W of 589 Na D2

light

55D. Whysong

Lick Laser

56

LICK LASER

M. Perrin

57

Na BeaconScattering by

mesospheric Na

layer at ~ 95 km

R ~ 8 mag

1.5’’ FWHM

Rayleigh back scatter

Maximum altitude of

Rayleigh ~ 35 km

48’’

58

Keck Observatory

Na 589 nm Lasers at Lick & Keck

Lick Observatory

59http://en.wikipedia.org/wiki/Image:Keck_laser_at_night.png

60

AU Mic Observed with Keck AO

Fitzgerald Kalas & Graham 2006

• Many debris disks are now observable

with Keck!

61

Conclusions

• Transient dust is common around may stars» Solar Zodiacal & Kuiper belts

» Beta Pic disk & other debris disk stars, e.g.,Fomalhaut & AU Microscopii

• Structure of debris disks gives hints of wheretheir planets orbit

• Optical properties of dust grains suggest thatplanets grow “bottoms up”

• Rapid progress in adaptive optics now makesit possible to image debris disks from theground» In the near future instruments such at the Gemini

Observatories “Planet Imager” will see planetsdirectly!

62

63

The End

top related