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Protoplanetary Disks
David J. Wilner
Harvard-Smithsonian Center for Astrophysics
May 24, 2005ly 26,
Astrobiology, McMaster University
1
Solar System Characteristics
Galileo: Sunspot Drawings (1613)
• planet orbits lie in a plane
• planet orbits nearly circular
• Sun’s rotational equator
coincides with this plane
• planets and Sun revolve in
same west-east direction
Copernicus: De Revolutionibus (1543)
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Equivalence of the Sun and Stars
Rene Decartes
1596- 1650
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Principia Philosophiae (1644):
Stars and Sun are the same and
formed from rotating vortices.
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Kant/Laplace Nebular Hypothesis
Gravitational contraction of a
slowly rotating gaseous nebula
makes a flat, spinning disk that
forms (rings then) planets.
Kant 1724-1801
Laplace 1749-1827
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Basic Questions
• How do disks form? What affects disk properties?
• How is angular momentum transported in disks?
• How do planets form in disks?
• Does environment influence disk evolution?
• Observables: size, mass, density, temperature,
ionization, composition, gas chemistry, dust
mineralogy, structure (flaring, warps, gaps), ...
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Stars Form in Molecular Cloud Cores
Taurus Molecular Cloud (optical)
(infrared)
Benson & Myers 1989
Dense Cores
(radio)
900 AU
Padgett et al. 1999
Barnard (1906)
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Schematic Solar System Formation
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Size Scales to Consider
Dutrey 2004
• nearest star forming regions with large samples of young
stars: 150 pc (Taurus, Ophiucus, Chameleon, Lupus,...)
– R ~ 400 AU disk
– R ~ 40 AU Kuiper Belt
– dR ~ 0.4 AU disk gap
~
~
~
3 arcsec
0.3 arcsec
0.003 arcsec
• subarcsecond angular scales are challenging to resolve
– “normal” optical/near-ir telescope, e.g. CFHT q ~ 0.5 arcsec
– large submm telescope, e.g. JCMT q ~ 7 arcsec (l/450 mm)
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Disk Observations
optical
infrared
submm • disks are natural multi-l
objects due to radial and
vertical gradients (n,T, ...)
star
TW Hya
HST/STIS
(G. Schneider)
dust
(1% of disk mass)
4’’
• optical: scattered light
– contrast, illumination
• infrared: warm dust & gas
TW Hya Weinberger et al. 2002
– near-ir: inner disk
– far-ir: only from space
• submm: cold dust & gas
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Infrared “Excess” Emission
• If the planetary material
of the Solar System were
crushed to ~mm sized dust
and spread out in a disk,
then its surface area
increases by ~1013x and
becomes easy to detect
as ir “excess” .
Spitzer Space Telescope
Barnard (1906)
Taurus Disks Hartmann et al. 2005
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Disk Frequency and Lifetime
• most (all) stars born
with circumstellar disks
(e.g. 3.4 mm excess)
~ 50% gone by 3 Myr
~ 90% gone by 5 Myr
• circumstellar dust
removed? or evolved?
Haisch, Lada, Lada 2001
• Spitzer will improve
statistics dramatically
(c2d and FEPS
Legacy Programs)
Barnard (1906)
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Disk around a Brown Dwarf
Luhman et al. 2005
• OTS44 (M9.5)
•
M* ~15 Mjup
•
L* ~0.001 L
• Spitzer: mid-ir
excess  disk
• Do miniature
Solar Systems
form around
brown dwarfs?
Barnard (1906)
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Resolved Disk Studies
• optical: scattered light
– high resolution (coronographic) imaging of surface
• near and mid-infrared spectroscopy
– rovibrational lines probe atmosphere < ~ few AU
– solid state features probe dust mineralogy
• near and mid-infrared interferometry
– detect dust emission at ~ AU scales (no imaging)
• far-infrared: no large apertures (in space)
• millimeter and submillimeter interferometry
– image dust and gas where most of mass resides
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Importance of Millimeter l’s
• bulk of disk material is “cold” H2
– Tk ~30 K at r ~100 AU for a typical T-Tauri star
• dust continuum emission has low opacity:
– dFn = Bn(T) knS dA, detect every dust particle
– millimeter flux ~ mass, weighted by temperature
– Mdisk~ 0.001 - 0.1 M (Beckwith et al. 1990)
• spectral lines of many trace molecules
– heterodyne dn/n >106: kinematics, chemistry
• many element interferometry enables imaging
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Millimeter Interferometry
OVRO
BIMA
NMA
IRAM PdBI
VLA
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SMA
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ATCA
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Dust Continuum Surveys
• IRAM PdBI 2.7 mm & 1.3 mm
–
–
q ~ 0.5 arcsec, mass limit ~ 0.001 M
model: S ~r-p, T ~r-q  p+q ~1.5, R > 150 AU
–
–
–
–
resolve disk elongations
find “large” disk sizes
confirm low dust opacities
“shallow” density profiles
(Dutrey, Guilloteau et al.)
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Physical Models of Disk Structure
• replace power-law
parameterizations with
self-consistent disk
models using radiative
and hydrostatic equil.
T~r-0.5
S~r-1
• accretion ~10-8 M/yr
 irradiated, flared
h(r)
SED
D’Alessio et al. 1998, 2001, …
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Testing Disk Models: TW Hya
data
• irradiated accretion disk model
matches SED, resolved data
model
SED
residual
Calvet et al. 2002
SMA 870 mm
VLA 7 mm
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Qi et al. 2004
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The Orion Proplyds
• “shadow” disks around low mass stars in Orion Nebula
Cluster (distance 450 pc) dramatically imaged by HST,
e.g. O’Dell et al. 1993, McCaughrean & Stauffer 1994, ...
UKIRT
• clusters are the common
star formation environment
• proplyds ionized by
q1 Ori C  evaporating
• optically opaque;
lower limits on mass
• are they viable sites of
Solar System formation?
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The Orion Proplyds (cont.)
• measure disk masses at long l’s where dust is optically thin
• interferometry essential: separate proplyds, filter out cloud
• previous nondetections
(BIMA Mundy et al. 1995;
OVRO Bally et al. 1998)
• new SMA 880 mm results:
four detections > 0.01 M
(standard assumptions)
• some proplyds have
sufficient bound material
to form Solar Systems
Williams, Andrews, Wilner 2005
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CO Line Observations
• CO is most abundant gas tracer of the “cold” H2
• low J rot. lines collisionally excited, thermalized
• optically thick: Tk(r) ~ r-q  q = 0.5 (flared)
• detailed kinematics: disk rotation, turbulence
12CO
J=2-1 IRAM PdBI ~ 15 systems, Simon et al. 2000
Doppler Shift
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CO Line Modeling
• results for 9 young stars from Simon et al. (2000)
• motions are Keplerian: v(r/D) = (GM*/r)0.5 sin i
• constrain M*, test stellar evolutionary tracks
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CO Line Modeling (cont.)
TW Hya SMA
12CO J=2-1,
Wilner et al. 2005
500 AU
• Keplerian velocity field
• disk size, inc., orientation
•
dvturb < 0.05 km/s
• use multiple lines to probe
Tk(r,z); excitation, abundance
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Protoplanetary Disk Origins
• Initial conditions from individual, isolated, dense cores
– ~few x M , <10 K, low turbulence (NH3 lines, e.g. Myers)
– centrally condensed: approach r ~r -2 (dust, e.g. Evans, Lada)
– slowly rotating: W ~ <10-14 to 10-13 s-1 (tracer v, e.g Goodman)
Caselli et al. 2002
N2H+(1-0) survey
• centrifugal barrier to collapse should be ~W2 t3
– expect wide range of disk sizes and masses
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Observing Embedded Disks
• Surrounding envelope complicates observational study
– where does envelope end and disk begin?
– additional kinematic components: infall and bipolar outflow
• Can we detect the youngest, smallest, protostellar disks?
VLA 7mm Rodriguez et al. 2004
JCMT 850 mm
10,000 AU
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30 AU
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Disks and Jets
• theory predicts intricate disk/jet connection
– e.g. Magnetocentrifugal X-wind (Shu et al. 1994)
• DG Tau: direct evidence of connection
–
13CO(2-1)
line wings show velocity gradient
in same sense as observed in [SII]/[OI] optical jet
Red
[SII]
Blue
Testi et al. 2002
Bacciotti et al. 2002
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Towards Nebular Chemistry: Submm
• submm molecular high-J rot.
lines and vibrational lines
– well matched to disks,
n~107 cm-3, T~100-1000 K
Kuan et al. 2005
– avoid confusion with envelope
• IRAS16293 with SMA:
complex “hot core” organic
molecules at < 400 AU
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Towards Nebular Chemistry: IR
• mid-infrared l’s
– absorption:
pencil beam for
edge-on geometry
– dn/n ~103
– ices, silicates,
PAHs,
– molecules:
H2, CH4, CO2, ...
• (a lot of) new data
from Spitzer IRS
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Protoplanetary Disk Chemistry
• single dish surveys of a handful of Keplerian disks detect
most abundant simple species like HCO+, HCN, H2CO, ...
TW Hya
JCMT
& CSO
Thi et al.
(2004)
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Protoplanetary Disk Chemistry (cont.)
• results of single dish surveys
– low spatial resolution, only sensitive to ~50 AU scales
– depletions 5 to >100x, at limits of current sensitivity
– ion-molecule reactions: HCO+, N2H+
– photochemistry important: high CN/HCN, C2H
– most emission arises in layer between photodissociated surface
and cold, depleted midplane (e.g. van Zadelhoff et al. 2003)
• interferometric imaging
– difficult but possible at 50 AU scales
– low TB for t < 1, Dv Doppler limited
– e.g. TW Hya SMA HCN(3-2)
150 AU
Qi et al., in prep
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Effects of Stellar Multiplicity
• millimeter fluxes lower for binary systems
• disk masses lower
• tidal truncation: disks within Roche lobes (Jensen et al. 1996)
• e.g. UZ Tau quadruple
– UZ Tau East
0.03
AU asin i binary: circumbinary
emission (typical of single star)
– UZ Tau West
50
AU binary: weak circumstellar
emission
– are disks aligned? coplanar?
OVRO Mathieu et al. 2000
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Disk Structure: Gaps and Holes
• infrared excess, accretion largely gone ~ few Myr
• spectral “gaps”: TW Hya, GM Aur, CoKu Tau 4, ...
• clearing from inside-out? planet formation?
5-20 mm
“gap”
20 AU
CoKu Tau 4
D’Alessio et al. 2005
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Quillen et al. 2004
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NASA Disk Evolution Movie
QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture.
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Atacama Large Millimeter Array
• large! ~64 x 12m (+12 x 7m) telescopes;
>10 km  < 0.02 arcsec at 870 mm
early science: 2008
full operation: 2012?
VertexRSI prototype
antenna, Socorro, NM
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Next Generation Submm Imaging
• hypothetical planet in TW Hya disk (Wolf & D’Angelo 2005)
simulated ALMA image
5 AU
Model density distribution
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From Dust to Planets: Grain Growth
Blum et al.
The beginning: dust particles stick together
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Millimeter Spectral Signatures
• observations at l probe
particle sizes ~O(l)
• Fmm~ kdust l-2 ~l-(b+2);
if t < 1, then observe b,
diagnostic of size
(shape, composition, ...)
b<1
b>1
• small, a << l, b = 2
large, a >> l, b = 0
• observe b ~ 1
– large grains? or t >1?
– need images to resolve
Sargent & Beckwith 1991
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Millimeter Spectrum: TW Hya
• Fmm~ kdust l-2
~l-2.6
• VLA 7mm resolves
emission w/low TB
t < 1, kdust ~ l-0.7
 large grains
amax = 1cm
• more resolved
disks with b<1
Natta et al. 2004
Calvet et al. 2002
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Dust Grows and Settles
• theory: expect particles to grow and settle to
midplane, develop bimodel size distribubution
Wilner et al. 2005
Weidenschilling 1997
~cm sizes in midplane
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TW Hya: VLA l3.5cm
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Summary
• gravity + angular momentum forms disks
• observations: complementary info mm’s to cm’s
• disk lifetime (infrared excess) ~ few Myr
• derived properties for ~1 Myr old disks
– typical Mdisk ~0.01 M ,(wide range)  protoplanetary
– Rdisk to ~100’s of AU
– velocity field is Keplerian (Mdisk<< M*)
– structure consistent with irradiated accretion models
– glimpses of nebular chemistry, dust evolution
• companions influence structure: truncation, gaps
• amazing prospects for the near future
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Kepler and the Nature of Stars
“You think that the stars are simple things,
and pure. I think otherwise, that they are
like our earth... in my opinion there is also
water on the stars... and living creatures as
well, who exist only because of these
earthlike conditions. Both that unfortunate
man Giordano Bruno, the same fellow who
was burned at the stake in Rome over hot
coals, and Brahe, of good memory, believed
that there are living creatures on the stars.”
Johannes Kepler
1571- 1630
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Letter from Kepler to Johann
Brengger, November 30, 1607
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