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Protoplanetary Disks

Protoplanetary Disks. David J. Wilner Harvard-Smithsonian Center for Astrophysics. 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.

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Protoplanetary Disks

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  1. Protoplanetary Disks David J. Wilner Harvard-Smithsonian Center for Astrophysics Astrobiology, McMaster University

  2. 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 Galileo:Sunspot Drawings (1613) Copernicus:De Revolutionibus (1543) Astrobiology, McMaster University

  3. Equivalence of the Sun and Stars Principia Philosophiae (1644): Stars and Sun are the same and formed from rotating vortices. Rene Decartes 1596- 1650 Astrobiology, McMaster University

  4. Kant/Laplace Nebular Hypothesis Gravitational contraction of a slowly rotating gaseous nebula makes a flat, spinning disk that forms (rings then) planets. Kant 1724-1801Laplace 1749-1827 Astrobiology, McMaster University

  5. 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), ... Astrobiology, McMaster University

  6. Taurus Molecular Cloud (optical) Benson & Myers 1989 Dense Cores (radio) (infrared) 900 AU Padgett et al. 1999 Barnard (1906) Stars Form in Molecular Cloud Cores Astrobiology, McMaster University

  7. Schematic Solar System Formation Astrobiology, McMaster University

  8. 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 q ~ 0.5 arcsec • large submm telescope, e.g. JCMT q ~ 7 arcsec (l/450 mm) Dutrey 2004 Astrobiology, McMaster University

  9. TW Hya Weinberger et al. 2002 Disk Observations optical infraredsubmm • disks are natural multi-l 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 star TWHya HST/STIS (G. Schneider) dust (1% of disk mass) 4’’ Astrobiology, McMaster University

  10. Spitzer Space Telescope 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” . Barnard (1906) Taurus Disks Hartmann et al. 2005 Astrobiology, McMaster University

  11. 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? • Spitzer will improve statistics dramatically (c2d and FEPS Legacy Programs) Haisch, Lada, Lada 2001 Barnard (1906) Astrobiology, McMaster University

  12. Luhman et al. 2005 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) Astrobiology, McMaster University

  13. 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 Astrobiology, McMaster University

  14. 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 • heterodynedn/n >106: kinematics, chemistry • many element interferometry enables imaging Astrobiology, McMaster University

  15. OVRO BIMA NMA IRAM PdBI VLA ATCA SMA Millimeter Interferometry Astrobiology, McMaster University

  16. 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.) Astrobiology, McMaster University

  17. S~r-1 T~r-0.5 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, … Astrobiology, McMaster University

  18. Testing Disk Models: TW Hya • irradiated accretion disk model • matches SED, resolved data SED residual model data Calvet et al. 2002 SMA 870 mm Qi et al. 2004 VLA 7 mm Astrobiology, McMaster University

  19. UKIRT • proplyds ionized by q1 Ori C  evaporating • optically opaque; lower limits on mass • are they viable sites of Solar System formation? 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, ... • clusters are the common star formation environment Astrobiology, McMaster University

  20. The Orion Proplyds (cont.) • measure disk masses atlong 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 Astrobiology, McMaster University

  21. 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 Astrobiology, McMaster University

  22. CO Line Modeling • results for 9 young stars from Simon et al. (2000) • motions are Keplerian: v(r/D) = (GM*/r)0.5sin i • constrain M*, test stellar evolutionary tracks Astrobiology, McMaster University

  23. CO Line Modeling (cont.) Model Data • Keplerian velocity field • disk size, inc., orientation • dvturb < 0.05 km/s • use multiple lines to probe Tk(r,z); excitation, abundance TW Hya SMA 12COJ=2-1, Wilner et al. 2005 500 AU Astrobiology, McMaster University

  24. 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) • centrifugal barrier to collapse should be ~W2 t3 • expect wide range of disk sizes and masses Caselli et al. 2002 N2H+(1-0) survey Astrobiology, McMaster University

  25. VLA 7mm Rodriguez et al. 2004 JCMT 850 mm 30 AU 10,000 AU 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? Astrobiology, McMaster University

  26. 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 Astrobiology, McMaster University

  27. 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 Kuan et al. 2005 Astrobiology, McMaster University

  28. 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 Astrobiology, McMaster University

  29. 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) Astrobiology, McMaster University

  30. 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 Astrobiology, McMaster University

  31. 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 Astrobiology, McMaster University

  32. 20 AU CoKu Tau 4 D’Alessio et al. 2005 Quillen et al. 2004 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” Astrobiology, McMaster University

  33. NASA Disk Evolution Movie Astrobiology, McMaster University

  34. 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 Astrobiology, McMaster University

  35. Next Generation Submm Imaging simulated ALMA image • hypothetical planet in TW Hya disk (Wolf & D’Angelo 2005) 5 AU Model density distribution Astrobiology, McMaster University

  36. From Dust to Planets: Grain Growth Blum et al. The beginning: dust particles stick together Astrobiology, McMaster University

  37. Millimeter Spectral Signatures • observations at  probe particle sizes ~O(l) • Fmm~ kdust l-2 ~l-(b+2);if t < 1, then observe b, diagnostic of size (shape, composition, ...) • small, a << l, b = 2 large, a >> l, b = 0 • observe b ~ 1 • large grains? or t >1? • need images to resolve b < 1 b > 1 Sargent & Beckwith 1991 Astrobiology, McMaster University

  38. Millimeter Spectrum: TW Hya • Fmm~ kdust l-2 ~l-2.6 • VLA 7mm resolves emission w/low TBt < 1, kdust ~ l-0.7  large grains • more resolved disks with b<1 Natta et al. 2004 amax = 1cm Calvet et al. 2002 Astrobiology, McMaster University

  39. 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 TW Hya: VLA 3.5cm Astrobiology, McMaster University

  40. 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 Astrobiology, McMaster University

  41. 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, 1607 Johannes Kepler 1571- 1630 Astrobiology, McMaster University

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