Download Circumstellar Disks: IRAS to ALMA (by way of HST) Dr. Karl Stapelfeldt

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)
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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
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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AndreAy/Ge
et al.
1993
5
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
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Smith & Terrile 1984
Debrisk disk dust must be constantly
replenished, as small grains are readily lost
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Disk Spectra and Statistics
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Infrared Space
Observatory (ISO)
• European Space Agency
Mission in low Earth
orbit
• 60 cm cryogenic
telescope
• Operated 1995-1998
• 2 spectrometers were
very productive
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ISO showed compositional link
between comets & disks
Tielens
et al.
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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 disks
disk formation typically complete after 0.9 Myrs; Evans et al. 2009
• Surveys of nearby star-forming regions find
lifetimes of 0.5 Myrs for
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Debris Disk Frequency from Spitzer Surveys
(Trilling et al. 2008)
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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)
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Common warm dust temperatures
(Morales et al. 2011)
FGK stars
A stars
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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
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• 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
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Geoff, Karl, & Chas
representing
The DUNES Team
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Resolved
disks
from
Herschel
DEBRIS
survey
(Booth et
al. 2013)
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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
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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
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High Resolution Disk Imaging
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 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
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Central 1600 AU of
edge-on
 Pictoris disk;
Kalas & Jewitt 1995
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HST Imaging of Orion
Silhouette Disks
(Bally et al. 2000)
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HST imaging of Edge-on
protoplanetary disks
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Bright debris disks now well-imaged
using coronagraphy
Left: HR 4976 A
ring with GPI,
Perrin et al. 2015
Right: HD 181327
ring, with HST,
Schneider et al.
2014
Left: AU
Mic edgeon disk
with HST,
Krist et al.
2005
Right: HD
32297 with
HST,
Schneider et
al. 2014
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HD 202628: G2 V star at 24 pc
Broad ring with central
clearing. Diameter of ~16
arcsec (400 AU).
Mean surface brightness
is 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
Krist et al. 2012
July 23, 2014
Sagan Summer School 2014
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New Processing of Archival HST
Debris Disk Images
HD 181327
Soummer et al. 2014
Big improvements in NICMOS
scattered light imagery
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HST followup of WISE Disks
New sample of bright debris disks; Padgett et al. 2015:
4/13 disks detected
1300 AU diameter
Ld/L* = 2.5 *10-3
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Adaptive optics disk images
HD 115600
Currie et al. 2015
HD 106906 Kalas et al. 2015
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Atacama Large Millimeter Array (ALMA)
the penultimate disk observatory
• 50 12-m antennas located at
16,000 ft plateau
• Offers sensitive imaging and
heterodyne spectroscopy
• Operating over 0.3- 9 mm
wavelength range
• Most competitive observatory in
the world today
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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
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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 ?
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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
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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
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Debris Disks and Exoplanets
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Herschel results for Dust luminosity
vs. presence of RV planets
(Bryden et al. 2014) but see also Marshall et al. 2015
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Systems known to have both planets and debris disks:
In most cases they are well-separated
Star
Fomalhaut
HR 8799
beta Pictoris
HD 38529
Epsilon Eridani
HD 216435
HD 202206
HD 50554
HD 10647
HD 19994
HD 128311
HD 82943
HD 52265
HD 38858
HD 142
HD 150706
HD 69830
70 Vir
61 Vir
HD 178911 B
Gl 581
HD 1461
HD 215152
HD 45184
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Planet orbital
semi-major axes
Outer Planet
Eccentricity
Disk inner
radius
Disk Resolved ?
115
15, 27, 43, 68
10
0.12, 3.70
3.4
2.56
0.83, 2.55
2.38
2.03
1.42
1.10, 1.76
0.75, 1.19
1.13
1.04
1
0.82
0.08, 0.19, 0.63
0.48
0.05, 0.22, 0.48
0.32
0.03, 0.04, 0.07, 0.22
0.11
0.09
0.06
0.11 ?
?
?
0.36
0.3-0.7 ?
0.07
0.27
0.42
0.1
0.3
0.25
0.22
0.29
0.27
0.37
0.38
0.07
0.4
0.35
0.12
0.38
0
0.38
0.3
133 AU
95 AU
30 AU
> 103 AU
2 AU, 35 AU
> 13 AU
> 50 AU
> 58 AU
~10 AU
> 7 AU
> 11 AU
> 65 AU
> 40 AU
~120 AU
> 28 AU
110 AU
1.0 AU
> 5 AU
~30 AU
> 28 AU
4 AU
> 49 AU
> 25 AU
> 70 AU
HST, IR, submm
IR
HST, IR, submm
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IR, submm
IR
HST, IR, submm
IR
IR
IR
IR
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Disks constrain planets
• 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)
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HD 69830 triple Neptune System


Old K0 star, d= 13 pc
Unusual population of
small/warm dust particles; major
recent collision ? (Beichman et al.
(Lisse et al. 2007)
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.
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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


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
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(Su et al. 2009)
see also
Chen et al. 2009,
Reidemeister et al. 2009
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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
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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
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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
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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
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Future large planetfinding telescope ?
Planet imagers will get disk observations for free
Community
studies now
beginning for
two flagship
mission
concepts
“HabEx” and
“LUVOIR“. To
be completed in
2019.
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Circumstellardisks.org
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