Circumstellar Disks: IRAS to ALMA (by way of HST)dmawet/teaching/circum...Wide Field Infrared Survey...

Circumstellar Disks:IRAS to ALMA (by way of HST)

Dr. Karl Stapelfeldt

JPL/Caltech

Talk overview

• History of space infrared astronomy

• Disk energy distributions, spectra, and statistics

• High resolution disk imaging

• Disks and exoplanets

• Future of Disk Studies

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InfraRed Astronomical Satellite (IRAS)

• First space infrared observatory

• 0.5 cm cryogenic telescope

• Operated in low Earth orbit for 10 months in 1983

• Primitive detectors limited spatial resolution to ~1 arcmin; mapping, not detailed imaging

• All-sky survey at 12, 25, 60, and 100 m (corresponding to material at 270, 130, 60, and 30 K)


The Legacy of IRAS

• Catalog of 500,000 sources seeded decades of high resolution imaging and spectroscopic work

• High scientific impact: to date more than 6,400 refereed papers have “IRAS” in the abstract

• At Caltech: IPAC and Morrisroe Astroscience building on S. Wilson Ave.

• Major results included starburst and ultraluminous IR galaxies (URLIRGS), interstellar cirrus, zodiacal dust bands, asteroid sizes, protoplanetary and debris disks.

• Major IRAS limitation was source confusion – often many objects blended together due to low spatial resolution

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IRAS Revealed Stages of Disk Evolution

Andre et al. 1993

IRAS was ideal for detecting the faint glow of cool circumstellar dust

IRAS found dust around more than 50% of young stars in nearby molecular clouds (for stars > 1 Lsun)

IRAS data allowed astronomers to classify young stellar objects according to IR spectral energy distribution

Molecular gas discovered in Class 0, I, and II disks in the 1990s, confirming they could be hosting planet formation

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Extrasolar debris disks were discovered by IRAS

measurement of stellar infrared excess:

• Found around nearby main-sequence

stars, mostly A type. The “Fabulous

four” Vega, Fomalhaut, Eridani,

and Pictoris

• Optically thin, gas-poor particle disks

but still 100- 10,000 times the dust of

the Sun’s interplanetary dust cloud

• Disk masses very small, < few lunar

masses. NOT protoplanetary disks.

• ~100 AU scales: Kuiper Belts

• Re-emitting 10-6

to 10-3

of the stellar

luminosity

• The best evidence for extrasolar

planetary systems prior to 1995 Smith & Terrile 198464/29/2016

Debrisk disk dust must be constantly

replenished, as small grains are readily lost



Disk Spectra and Statistics

84/29/2016

Infrared Space

Observatory (ISO)

• European Space Agency

Mission in low Earth

orbit

• 60 cm cryogenic

telescope

• Operated 1995-1998

• 2 spectrometers were

very productive


ISO showed compositional link

between comets & disks


Tielens

et al.


Spitzer Space Telescope

• 85 cm beryllium telescope, 6.5 m diffraction limit

• Operated cold 2003-2009, continues warm operation today

• Two science cameras (IRAC and MIPS), plus a low/moderate resolution spectrograph (IRS); 3< < 180 m. Efficient mapping

• Earth-trailing solar orbit

• 10-1000x more sensitive than 1983 IRAS mission

• Targeted observations, not a sky survey

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Ophiuchus star-forming region (Padgett et al. 2008)

Spitzer statistics of young disksdisk formation typically complete after 0.9 Myrs; Evans et al. 2009

• Surveys of nearby star-forming regions find lifetimes of 0.5 Myrs for


Debris Disk Frequency from Spitzer Surveys(Trilling et al. 2008)


A star 24 m excesses vs. time: decay 1/t over

~200 Myr; but many stars of all ages have little

or no excess. (Rieke et al. 2005)


Common warm dust temperatures(Morales et al. 2011)

A stars

FGK stars


Europe's Herschel Space Observatory

• 3.5 meter primary mirror

• Operated 2009-2013

• 70 m imaging resolution 4x sharper than Spitzer; resolving central holes & disk asymmetries

• Sensitivity to lower levels of LIR/Lstar at 100 & 160 m

• 600 nearby targets surveyed by DUNES and DEBRIS key programmes, plus ~200 others in small GO projects


Geoff, Karl, & Chas

representing

The DUNES Team


• Herschel project to survey 200 nearby solar-type stars at 100 & 160 m

• Excess detected in up to 20% of the targets, with examples seen down to a few times Kuiper Belt dust level

• Many disks resolved in Herschel’s 6” beam

Resolved

disks

from

Herschel

DEBRIS

survey

(Booth et

al. 2013)

Ay/Ge 198 Exoplanets 194/29/2016

Wide Field Infrared Survey Explorer


• Mission similar to IRAS but with

modern array detectors

• Sensitivity ~100 times better and

resolution 10x better than IRAS

• 40 cm telescope, low Earth orbit

• All-sky survey at 3.6, 4.5, 12, and

22 m

• Launched late 2009, operated in

all 4 bands to fall 2010.

• Continues operation at two

shortest wavelengths as NEOWISE


WISE all-sky survey finds field stars

with warm debris disks

~400 Hipparcos main sequence stars within 120 pc show 22 um excess > 0.25 mag (Padgett et al. )

Warm excess sources are likely young – exoplanet imaging targets

Below left: sky distribution of excess sources. Below right: 22 um excess frequency vs. spectral type


High Resolution Disk Imaging

224/29/2016


Pictoris: A hard act to follow

• 1984 coronagraphic detection in

visible light of edge-on disk around

a bright, nearby IRAS source

• No other debris disks detected in

scattered light for 15 years after

IRAS

• Beta Pic now recognized as

exceptionally young (20 Myrs) and

dusty

• Imaging of other disks prevented

by seeing-limited image quality:

needed HST and adaptive optics to

make progress in scattered light

imaging

Central 1600 AU of

edge-on

Pictoris disk;

Kalas & Jewitt 1995

234/29/2016

HST Imaging of Orion

Silhouette Disks


(Bally et al. 2000)

HST imaging of Edge-on

protoplanetary disks



Bright debris disks now well-imaged

using coronagraphy

26

Left: HR 4976 A

ring with GPI,

Perrin et al. 2015

Right: HD 181327

ring, with HST,

Schneider et al.

2014

Left: AU

Mic edge-

on disk

with HST,

Krist et al.

2005

Right: HD

32297 with

HST,

Schneider et

al. 2014

4/29/2016

Broad ring with central clearing. Diameter of ~16 arcsec (400 AU).

Mean surface brightnessis V ~ 24 mag arcsec-2 :Faintest debris disk yet detected with HST.

Clearly asymmetric:Inner edge is 139 AU from star in the NW, 161 AU in the SE.

Star is offset from ring center by 0.8ˮ (20 AU) –Eccentric ring

HD 202628: G2 V star at 24 pc

July 23, 2014 Sagan Summer School 2014

Krist et al. 2012

27

New Processing of Archival HST

Debris Disk Images

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Soummer et al. 2014

Big improvements in NICMOS

scattered light imagery

28

HD 181327

HST followup of WISE Disks

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1300 AU diameter

Ld/L

* = 2.5 *10

-3

New sample of bright debris disks; Padgett et al. 2015:

4/13 disks detected

4/29/2016

Adaptive optics disk images


HD 115600

Currie et al. 2015

HD 106906 Kalas et al. 2015

Atacama Large Millimeter Array (ALMA)

the penultimate disk observatory

• 50 12-m antennas located at

16,000 ft plateau

• Operating over 0.3- 9 mm

wavelength range


• Offers sensitive imaging and

heterodyne spectroscopy

• Most competitive observatory in

the world today

Key ALMA disk imaging results I.

Fomalhaut debris ring

(Boley et al. 2012)

• 870 m continuum image with 1

resolution

• Shows narrower ring than in HST

images: large particles trace

parent bodies. Further evidence

for shepherding planets

• Unable to map at higher

resolution due to low surface

brightness


Key ALMA disk imaging results II.

HL Tauri disk

• 1 Myr old embedded

young star. Long-known

disk inclined 40°

• 14 AU resolution image

in submm continuum

• Disk radius ~140 AU

• Intricate structure of

ring-like density contrasts

• Regions of enhanced grain

growth?

• Gaps cleared in outer disk

by planets ?


Key ALMA disk

imaging results III.

Asymmetric Transition disks

(van der Marel et al. 2016)

• Central holes seen both gas and

dust distribution. Gas holes are

smaller, suggesting planetesimal

formation

• Dust ring brightness is not

uniform. Azimuthal peaks

theorized to be dust traps

where enhanced grain growth

is taking place


Key ALMA disk imaging results IV.

Highest resolution image

of protoplanetary disk

TW Hydrae

(Andrews et al. 2016)

• 8 Myr old face-on disk

• Resolution of 30 mas

surpasses Hubble

• Radial gap structure

reminiscent of HL Tauri

• Central hole a few AU across:

gap cleared by planets ?

Prime ELT coronagraph target



Debris Disks and Exoplanets

364/29/2016


Herschel results for Dust luminosity

vs. presence of RV planets

(Bryden et al. 2014) but see also Marshall et al. 2015

374/29/2016


Systems known to have both planets and debris disks:

In most cases they are well-separated

Star Planet orbital Outer Planet Disk inner Disk Resolved ?

semi-major axes Eccentricity radiusFomalhaut 115 0.11 ? 133 AU HST, IR, submm

HR 8799 15, 27, 43, 68 ? 95 AU IR

beta Pictoris 10 ? 30 AU HST, IR, submm

HD 38529 0.12, 3.70 0.36 > 103 AU

Epsilon Eridani 3.4 0.3-0.7 ? 2 AU, 35 AU IR, submm

HD 216435 2.56 0.07 > 13 AU

HD 202206 0.83, 2.55 0.27 > 50 AU

HD 50554 2.38 0.42 > 58 AU IR

HD 10647 2.03 0.1 ~10 AU HST, IR, submm

HD 19994 1.42 0.3 > 7 AU

HD 128311 1.10, 1.76 0.25 > 11 AU IR

HD 82943 0.75, 1.19 0.22 > 65 AU

HD 52265 1.13 0.29 > 40 AU

HD 38858 1.04 0.27 ~120 AU IR

HD 142 1 0.37 > 28 AU

HD 150706 0.82 0.38 110 AU

HD 69830 0.08, 0.19, 0.63 0.07 1.0 AU

70 Vir 0.48 0.4 > 5 AU

61 Vir 0.05, 0.22, 0.48 0.35 ~30 AU IR

HD 178911 B 0.32 0.12 > 28 AU

Gl 581 0.03, 0.04, 0.07, 0.22 0.38 4 AU IR

HD 1461 0.11 0 > 49 AU

HD 215152 0.09 0.38 > 25 AU

HD 45184 0.06 0.3 > 70 AU

384/29/2016

Disks constrain planets

3

9Ay/Ge 198 Exoplanets

• Presence of IR excess indicates small colliding

small bodies in a planetary system

• Imaged disk provides system inclination and

localizes where planets may be seen

• Sharpness of disk edge constrains planet

mass, if planet is also imaged

• Disks Azimuthal variations also trace planet

mass [Right: cases of 1 Me and 5 Me planet

gravitational effects on warm dust

distribution, Stark et al. 2009]

• Perturbed outer disks are only means to

detect low-mass outer planets (evidenced

again by proposed Planet IX in our system)


HD 69830 triple Neptune System

Old K0 star, d= 13 pc

Unusual population of

small/warm dust particles; major

recent collision ? (Beichman et al.

2005)

Planets at 0.08, 0.19, 0.63 AU

(Lovis et al. 2006)

Detailed dust size/composition

analysis & radiative balance

places the dust belt at ~1 AU,

exterior to planets.

Parent bodies would be

dynamically stable there.

(Lisse et al. 2007)


Four planets orbiting HR 8799

Marois et al. 2008, 2010

A0 star at 40 pc distance

Young system age ~60 Myrs

Spectra of outer 3 below

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The HR 8799 Debris Disk

(Su et al. 2009)

see also

Chen et al. 2009,

Reidemeister et al. 2009

Infrared excess shows two

blackbody-like

components

Simple blackbody grains

would produce this if

located in belts at

9 AU (T= 150 K)

95 AU (T= 45 K)

Dynamically viable: This

places the dust interior

and exterior to the

planets imaged at 15, 27,

43, 68 AU

424/29/2016


Disk/planet arrangement in

the HR 8799 system

Planet e wasfound in the gap between inner belt and planet d Suggestion that belt edges may be located at major resonances Planet orbits still being defined

Marois et al. 2010

434/29/2016

The state of disk science

• Protoplanetary and debris disks appear to be common;

consistent with Kepler results for planet frequency

• Protoplanetary disks dissipate by 10 Myrs, and debris

disk brightness decays quickly over a few hundred Myrs

• Disk sizes are comparable to the Kuiper Belt, radii of

~100 AU. Central holes are apparent by ages of a few

Myrs

• Debris disks often have 2 planetesimal belts. Their

structures include gaps, warps, and asymmetries

indicative of planetary perturbations, but number of

imaged systems showing this is still small

• There at least as many known disks as stars hosting

exoplanets


Future of Disk Studies

• Comprehensive ALMA studies of disk structure,

chemistry, and evolution

• Resolve more examples of small disks with

SPHERE, GPI, and future ELTs. Directly image

protoplanets in disks and observe interactions

• Assess exozodiacal dust as noise source for future

direct imaging of habitable exoplanets

• High contrast imaging on optical space

telescopes will provide best sensitivity to

tenuous debris disks and mature planets



Large Binocular Telescope

Interferometer

Twin 8.4m telescopes at Univ. of

Arizona

NASA-funded 10 µm nulling

interferometer instrument

Survey of habitable zone dust

around nearby stars

Expected sensitivity down to 10

“zodis”

Results will drive design of future

planet finders

Progress slowed by telescope

issues

Future large planet-

finding telescope ?


Community

studies now

beginning for

two flagship

mission

concepts

“HabEx” and

“LUVOIR“. To

be completed in

2019.

Planet imagers will get disk observations for free

Circumstellardisks.org


Circumstellar Disks: IRAS to ALMA (by way of HST)dmawet/teaching/circum...Wide Field Infrared Survey...

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