May 24, 2005ly 26, 2004 Astrobiology, McMaster University1 Protoplanetary Disks David J. Wilner...

May 24, 2005ly 26, 2004

Astrobiology, McMaster University 1

Protoplanetary DisksDavid J. Wilner

Harvard-Smithsonian Center for Astrophysics

May 24, 2005ly 26, 2004


Solar System Characteristics

• 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)

Galileo: Sunspot Drawings (1613)

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Equivalence of the Sun and Stars

Principia Philosophiae (1644): Stars and Sun are the same and formed from rotating vortices.

Rene Decartes 1596- 1650

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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 CoresTaurus Molecular Cloud (optical)

Barnard (1906)

Benson & Myers 1989

Dense Cores (radio)

(infrared)

Padgett et al. 1999900 AU

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Schematic Solar System Formation

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Size Scales to Consider

• nearest star forming regions with large samples of young stars: 150 pc (Taurus, Ophiucus, Chameleon, Lupus,...)– R ~ 400 AU disk ~ 3 arcsec

– R ~ 40 AU Kuiper Belt ~ 0.3 arcsec– dR ~ 0.4 AU disk gap ~ 0.003 arcsec

• subarcsecond angular scales are challenging to resolve– “normal” optical/near-ir telescope, e.g. CFHT ~ 0.5 arcsec– large submm telescope, e.g. JCMT ~ 7 arcsec (/450 m)

Dutrey 2004

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• disks are natural multi- objects due to radial and vertical gradients (n,T, ...)

• optical: scattered light– contrast, illumination

• infrared: warm dust & gas– near-ir: inner disk – far-ir: only from space

• submm: cold dust & gas

Disk Observations

TW Hya Weinberger et al. 2002

star

optical infrared submm

dust(1% of disk mass)

TW HyaHST/STIS

(G. Schneider)4’’

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Infrared “Excess” Emission• If the planetary material

of the Solar System were crushed to ~m sized dust and spread out in a disk, then its surface area increases by ~1013x and becomes easy to detect as ir “excess” .

Barnard (1906)Taurus Disks Hartmann et al. 2005

Spitzer Space Telescope

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Disk Frequency and Lifetime• most (all) stars born with

circumstellar disks (e.g. 3.4 m excess)

~ 50% gone by 3 Myr ~ 90% gone by 5 Myr• circumstellar dust

removed? or evolved?

• Spitzer will improve statistics dramatically (c2d and FEPS Legacy Programs)

Barnard (1906)

Haisch, Lada, Lada 2001

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Disk around a Brown Dwarf

• 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)

Luhman et al. 2005

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• 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

Resolved Disk Studies

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Importance of Millimeter ’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:

– dF= B(T) 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 >106: kinematics, chemistry

• many element interferometry enables imaging

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Millimeter Interferometry

OVRO BIMA

NMA

IRAM PdBI

VLASMA ATCA

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Dust Continuum Surveys• IRAM PdBI 2.7 mm & 1.3 mm

– ~ 0.5 arcsec, mass limit ~ 0.001 M – model~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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T~r-0.5 ~r-1

h(r)

SED

Physical Models of Disk Structure

• replace power-law parameterizations with self-consistent disk models using radiative and hydrostatic equil.

• accretion ~10-8 M/yr irradiated, flared

D’Alessio et al. 1998, 2001, …

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Testing Disk Models: TW Hya

Qi et al. 2004

• irradiated accretion disk model matches SED, resolved data

SMA 870 m

VLA 7 mm

resi

dual

m

odel

da

ta

Calvet et al. 2002

SED

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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 1

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 atlong ’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 m 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, turbulence12CO 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.)

• Keplerian velocity field

• disk size, inc., orientation

• vturb < 0.05 km/s

• use multiple lines to probe Tk(r,z); excitation, abundance

TW Hya SMA 12CO J=2-1, Wilner et al. 2005

Mod

el

Dat

a

500 AU

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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 -2 (dust, e.g. Evans, Lada)

– slowly rotating: ~ <10-14 to 10-13 s-1 (tracer v, e.g Goodman)

• centrifugal barrier to collapse should be ~2 t3

– expect wide range of disk sizes and masses

Caselli et al. 2002 N2H+(1-0) survey

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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?

JCMT 850 m

10,000 AU 30 AU

VLA 7mm Rodriguez et al. 2004

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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

Blue

Bacciotti et al. 2002

[SII]

Testi 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

– avoid confusion with envelope

• IRAS16293 with SMA: complex “hot core” organic molecules at < 400 AU

Kua

n et

al.

2005

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Towards Nebular Chemistry: IR

• mid-infrared ’s– absorption:

pencil beam for edge-on geometry

– ~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 < 1, v Doppler limited

– e.g. TW Hya SMA HCN(3-2) Qi et al., in prep

150 AU

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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?

Quillen et al. 2004

20 AU

CoKu Tau 4D’Alessio et al. 2005

5-20 m“gap”

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NASA Disk Evolution Movie

QuickTime™ and aMPEG-4 Video decompressorare needed to see this picture.

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early science: 2008 full operation: 2012?

Atacama Large Millimeter Array• large! ~64 x 12m (+12 x 7m) telescopes;

>10 km < 0.02 arcsec at 870 m

VertexRSI prototype antenna, Socorro, NM

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Next Generation Submm Imaging

• hypothetical planet in TW Hya disk (Wolf & D’Angelo 2005)

Model density distribution

simulated ALMA image

5 AU

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From Dust to Planets: Grain Growth

The beginning: dust particles stick together

Blum et al.

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Millimeter Spectral Signatures

• observations at probe particle sizes ~O()

• Fmm~ dust -2 ~-(+2);

if < 1, then observe , diagnostic of size (shape, composition, ...)

• small, a << , = 2 large, a >> , = 0

• observe ~ 1– large grains? or >1?

– need images to resolve

Sargent & Beckwith 1991

< 1 > 1

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• Fmm~ dust -2

~-

• VLA 7mm resolves emission w/low TB < 1, dust ~ -0.7 large grains

• more resolved disks with <1 Natta et al. 2004

Calvet et al. 2002

amax = 1cm

Millimeter Spectrum: TW Hya

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~cm sizes in midplane TW Hya: VLA 3.5cm

Dust Grows and Settles

Weidenschilling 1997

• theory: expect particles to grow and settle to midplane, develop bimodel size distribubution

Wilner et al. 2005

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Summary• gravity + angular momentum forms disks

• observations: complementary info m’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.”Letter from Kepler to Johann Brengger, November 30, 1607Johannes Kepler

1571- 1630

May 24, 2005ly 26, 2004 Astrobiology, McMaster University1 Protoplanetary Disks David J. Wilner...

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