Transcript ppd_hia
Protoplanetary Disks David J. Wilner (CfA) “protoplanetary” properties Aug 22, 2006 grain growth disk gaps & protoplanets 1 Collaborators U. Michigan E. Bergin N. Calvet L. Hartmann NRAO IfA J. Williams S. Andrews M. Claussen C. Chandler Leiden CfA C. Qi T. Bourke M. Hughes M. Hogerheijde Heidelberg J. Rodmann T. Henning Arcetri A. Natta L. Testi UNAM P. D’Alessio 2 Molecular Clouds Disks Taurus Dark Cloud Barnard (1906) L1527 Protostars 2000 AU Benson & Myers 1989 Spitzer c2d T. Bourke Dense Cores Copernicus 1543 3 Schematic Solar System Evolution 10 105 yr protostar + primordial disk Lstar planet building protoplanetary disk 107 yr 109 yr 1 104 yr planetary system + debris disk 100 AU cloud collapse 8,000 5,000 2,000 Tstar (K) adapted from Beckwith & Sargent 1996, Nature, 383, 139 4 Schematic Solar System Evolution 10 Lstar planet building protoplanetary disk 107 yr 1 100 AU 8,000 5,000 2,000 Tstar (K) adapted from Beckwith & Sargent 1996, Nature, 383, 139 5 Observational Challenges • bulk of disk mass is “cold” (and dark) H2 – probed only through minor constituents – solids: thermal emission, scattered light – gas: trace species, subject to excitation and chemistry • angular scales are small, difficult to image – nearest regions with large samples at d=140 pc, e.g. Taurus, Ophiucus, Lupus, Chamaeleon, ... R (AU) (arcsec) outer disk 200 ~ 1.4 Kuiper Belt 40 ~ 0.3 disk gap 0.4 ~ 0.003 6 Disk n,T,... f(r,z): Panchromatic x-ray uv optical hot gas/accretion starlight mid-ir far-ir submm mm cm warm gas & dust cool gas & dust star dust (1% of disk mass) 4’’ HST TW Hya K8V d=56 pc Calvet et al. 2002 7 Characterizing Large Samples: SEDs • easy to detect warm (~900 K) mm size dust in near-ir (t ~1 for ~MCeres) • no confusion Barnard (1906) Spitzer Space Telescope Hartmann et al. 2005 8 Disk Frequency and Lifetime • most (all?) stars born with circumstellar disks, e.g. 3.4 mm excess (Haisch, Lada & Lada 2001) ~ 50% gone by 3 Myr ~ 90% gone by 5 Myr large dispersion • Spitzer (e.g. FEPS): most of the action in protoplanetary disk evolution is < 5 Myr Hillenbrand 2005 (Meyer et al.) log(age) 9 Protoplanetary Disk Masses • millimeter l’s: dust emission has low opacity – dFn = Bn(T) knS dA – millimeter flux ~ mass, weighted by temperature Mdisk Fn = 0.03 M 1 Jy ( 2 D 100 pc ) ( 3 50 K l T 1.3 mm ) 0.02 cm2 gm-1 k1.3mm – Mdisk<0.001 - 0.1 M (Beckwith et al. 1990) - 0.1 M disk mass ~F850mm - 0.001 M log(star mass) log(age) Andrews & Williams 2005 10 Environment: the Orion “Proplyds” • clusters are the common star formation environment • proplyds ionized by 1 Ori C evaporating • SMA observations: 4 proplyds: M > 0.01 M 18 upper limits (<M> ~0.001 M) • disks truncated? Williams, Andrews, Wilner 2005 11 Resolved Dust Emission • routine imaging of classical T-Tauri, Herbig Ae stars: > 0.7 arcsec, mass limit ~ 0.001 M (~40 sources) • e.g. IRAM Taurus 2.7/1.3 mm (Dutrey et al. 2001) – – – – resolve disk elongations simple model: S ~r-p, T~r-q “large” disk sizes: R>150 AU “shallow” surface density distributions: p+q ~ 1.5 12 Physical Models of Disk Structure • replace arbitrary power-laws with selfconsistent radiative and hydrostatic equilibrium • accretion < 10-8 M/yr irradiated, flared Kenyon & Hartmann 1987, Chiang & Goldreich 1997, 99 D’Alessio et al. 1997, 98, 01, ... Dullemond et al. 2000, 02, ... S~r-1 Tm~r-0.5 D’Alessio et al. 2001 H~r1.25 SED . steady a accretion: S ~ m/3pn ~ (r3/2Tm) -1 13 Testing Disk Structure Models • TW Hya: d=56 pc (unique) • irradiated accretion disk model – fits complete SED – matches resolved mm data, size scales ~10 to 200 AU SMA 870 mm Qi et al. 2004 VLA 7 mm data SED residual Calvet et al. 2002 14 Resolved Line Observations • CO is the most abundant gas tracer of H2 • CO lowest J rot. lines collisionally excited, thermalized – very optically thick: Tk(r) ~ r-q q = 0.5 - 0.6 (flared) – dn/n > 106: detailed kinematics (e.g. Simon et al. 2000) SMA: TW Hya HD163296 HD169142 15 Keplerian: v(r/D)= (GM*/r)0.5 sin i SMA HD 163296 C B A D A B C D 16 TW Hya Line Modeling • analyze with 2D radiative transfer and 2 minimization n,T: f(r,z) v(r) + R = 17210 AU, i = 6 1 deg, M*, dvturb, X(CO), ... SMA Model Doppler Shift 17 Gas vs. Dust Temperature • CO J=3-2, 6-5 stronger than SED model predicts SMA TW Hya • higher gas temperatures required in upper disk atmosphere to match – effect of x-rays? (Glassgold & Najita 2001) – mechanical heating? Qi et al. 2006 18 Towards Nebular Chemistry • simple species detected in a handful of disks (e.g. Kastner et al. 1997, Dutrey et al. 1998, Thi et al. 2003) – (global) depletions 5 to >100x, at limits of current sensitivity – ion-molecule reactions (HCO+) – photochemistry (HCN/CN) – deuteration (DCO+) Aikawa 2006 • rich chemistry – organics (H2CO) – starting to image, e.g. TW Hya HCO+(3-2) SMA 19 Protoplanetary Disk Properties • Plenty of Dust (SEDs, silicate features) • Gas rich (accretion, flared shapes) • Masses: 0.001 to 0.1 M (mm dust emission) • Sizes: 10’s- 100’s AU (CO, dust, scattered light) • Kinematics: Keplerian rotation (CO lines) • Lifetimes: few Myr (near-ir/mid-ir/mm statistics) all we need to form planets 20 NASA Disk Evolution Movie QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture. 21 The Rocky Road to Planethood 22 The Beginning: Particles Stick QuickTime™ and a YUV420 codec decompressor are needed to see this picture. SiO2 C. Dominik Blum et al. 1998, 2000 • collisional growth – sub-mm to cm size dust sticks at <1 m/s relative velocities 23 Spatially Resolved Scattered Light TW Hya HST/STIS • gray scattered light, r ~ 40 -150 AU • “large” scattering particles >> l ~1 mm Roberge et al. 2005 24 Millimeter Spectral Signatures • abs. coeff: k ~ l-b • diagnostic of dust size (see Draine 2006) – a << l, b = 2 (ism dust) – a >> l, b = 0 (pebbles) b~1 b>1 • if low opacity and R-J, then Fl~ k l-2~ l-(b+2) • at mm l’s, find b ~1 – grain growth? – partly optically thick? Beckwith & Sargent 1991 25 Grain Growth or Optical Depth? e.g. UX Ori, CQ Tau: a1.1-7mm~ 2.0, 2.6 b ~ 0 and large RD ? any b and small RD ? Testi et al. 2001 26 Ambiguity Resolved Rodmann et al. 2006 • VLA 7 mm: large R, low TB, small corrections for plasma t < 1 large grains – TW Hya: Calvet et al. 2002 – CQ Tau: Testi et al. 2003 – 11 Taurus disks (barely) resolved, most b1.3-7mm ~ 1 27 Complexity in Interpretation of b • b is an “average” k1mm for any dust model • for size power law n(a) ~a-q, amin<a< amax b 0 for large amax only if q < 3 • does agglomeration result in a power law? b1-7mm q=4.0 2 1 q=2.5 0 amax Natta et al. 2004 28 Grain Growth and Settling decrease dust/gas in upper layers population of ~cm size grains in midplane t=0 Weidenschilling 1997 29 TW Hya lcm Emission • dust disk model underpredicts 3.5 cm emission • ionized protostellar wind? – if Fcm dMacc/dt, then ~0.2 mJy • spinning dust? (Rafikov 2006) – requires unrealistic Carbon fraction in nanoparticles/PAHs • nonthermal? – X-rays (Kastner et al. 1997) – 3.5 cm apparently variable (upper limit of Rucinski 1992) 30 TW Hya: X-rays from Accretion • not scaled up solar-type magnetic activity (Kastner et al. 2002, Stelzer & Schmitt 2004) • plasma conditions unlike stellar coronae – n ~ 1013 cm-3, ~100x denser – T ~ 3 MK, (comparatively) cool • peculiar chemical abundances – metals depleted – N, Ne enhanced accreting, depleted gas, decoupled from dust 31 TW Hya: Evidence for “Pebbles” • 3.5 cm radio emission – not variable: weeks to years – resolved at ~ arcsec scale – low brightness ~10 K – steep spectrum to 6 cm dust emission from disk small + ~cm size dust Wilner et al. 2005 32 Remarks on Grain Growth • compelling evidence for growth (and processing) – most of original dust mass in mm/cm size particles • no clear trends with any stellar properties – mass ~5x, luminosity ~250x, age ~10x – no “evolutionary” trends (early active phase?) • mm/cm sizes persist for Myrs – planetesimal formation not efficient as predicted? – competition between agglomeration and collisions? • are the disks we can study the ones that will never form planets? (no: transitional objects) PPV: Natta, Testi, Calvet, Henning, Waters & Wilner, astro-ph/0602041 33 Infrared Gaps: Disk Clearing? • inner holes result in infrared flux deficits, e.g. TW Hya, CoKu Tau 4, GM Aur, DM Tau, ... r~4 AU wall at outer edge of gap Bryden et al. 1999 “gap” Calvet et al. 2002 inner disk with bit of ~mm dust 34 Photoevaporation Models • evaporation at R>Rg, where gas is no longer bound (Clarke et al. 2001, Matsuyama et al. 2003, Takeuchi et al. 2005, Alexander et al. 2006a,b) accretion rate – Rg ~ few AU for T-Tauri stars – open gap at Rg when evaporation rate ~ accretion (“uv switch”) gap time Clarke et al. 2001 radius 35 Protoplanets and Gaps • protoplanet-disk interaction transfers angular momentum, opens radial gap around protoplanet orbit – subsequent evolution: (mostly) cleared inner hole • active area: viscosity not understood, disk structure not known (and inbalance of torques leads to planet migration) Takeuchi et al. 1996 36 A Gap in Saturn’s Rings • Moon (S/2005 S1) in Keeler Gap, Cassini (May 1, 2005) • zero pressure, low viscosity, clean gap 37 Skepticism about Disk Gaps • complexity, degeneracy of geometry and opacity – spectral gap need not imply physical gap “... we remain skeptical of the existence of such a large central gap devoid of dust.” - Chiang & Goldreich (1999) “While wide gaps may exist in certain [protoplanetary] systems, SEDS do not provide convincing proof of their existence-perhaps millimeter wave imaging... may someday provide vivid evidence for the presence of disk gaps.” - Boss & Yorke (1996) 38 The GM Aur Infrared Gap Calvet et al. 2005 HST/NICMOS Schneider et al. 2002 IRAM CO(2-1) • ~ 2 Myr, M*=0.84 M Rdisk ~ 525 AU . • Macc ~ 10-8 M/yr • Spitzer IRS 5-40 mm requires inner hole radius ~ 24 AU ! 39 GM Aur: Submm Imaging HST NICMOS Wilner et al. 2006 40 Next Generation lmm-cm Facilities • 100x better sensitivity, resolution, image quality • global partnerships to fund ~$1B construction • Atacama Large Millimeter Array (l 300 mm-1 cm) – Key Science Goal: I. Image protoplanetary disks, to study their physical, chemical, and magnetic field structures, and to detect tidal gaps... – early science 2010? full operation 2013? • Square Kilometer Array (l 1 cm-3 m) – Key Science Project I. Cradle of Life: (a) thermal imaging at 0.001 arcsec to study terrestrial planet formation and disk evolution on sub-AU scales, (b) SETI – technologies in development 2020? 41 At the Limits of ALMA: Protoplanets • hypothetical planet in TW Hya disk simulated ALMA 900 GHz image (Wolf & D’Angelo 2005) 5 AU model density distribution 42 New Territory for SKA • thermal emission at ~1 mas resolution with short l cm capability and ~1000 km baselines • track grain growth in inner disk to pebbles – observe radial gradients, settling – concentrations of pebbles? vortices? • unprecedented sub-AU views – low opacity, even in terrestrial zone – direct detection of tidal gaps – orbital timescales of inner disk ~ 1 year track secular changes (“movies”) HST NICMOS 43 Summary • observed disk properties are “protoplanetary” – – – – – Rdisk to ~ 100’s of AU typical Mdisk ~ 0.01 M ,(wide range) Keplerian velocity fields SEDs & structure match irradiated accretion models inner/outer disk lifetime ~ few Myr • starting to observe aspects of planet building – grain growth leading to small rocks – constituents similar to proto-Solar nebula – firm evidence for gaseous inner disk holes • major new facilities on the horizon – amazing prospects with 100101 mas resolution 44 End 45 The Whirlpools of Descartes Rene Decartes 1596- 1650 Principia Philosophiae (1644) stars and Sun are the same, existing in rotating “vortices” (tourbillons) 46 Environment: the Proplyds • “proplyds” = disks around low mass stars in Orion Nebula Cluster dramatically imaged by HST (O’Dell et al. 1993) UKIRT HST • 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? 47 Proplyd Masses • previous nondetections (BIMA Mundy et al. 1995; OVRO Bally et al. 1998) • SMA observations: 4 proplyds: M > 0.01 M 18 upper limits (<M> ~0.001 M) • disks truncated? Williams, Andrews, Wilner 2005 48 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 49 Gas: Accretion vs. Stellar Age measuring disk accretion rates evolution of accretion Muzerolle et al. 2000 50 Basic Questions • How do disks form? What affects disk properties? • How is angular momentum transported in disks? • How and when do planets form in disks? • How does environment influence disk evolution? • Observables: size, mass, density, temperature, ionization, composition, gas chemistry, dust mineralogy, structure (flaring, warps, gaps), ... 51 Solar System Characteristics • fossil record disk origin – 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 • What are initial conditions? • How do planets form? Copernicus 1543 • What accounts for diversity of planetary systems? 52 Observational Challenges • bulk of disk mass is “cold” (and dark) H2 – probed only through minor constituents • dust: thermal emission, scattered light • trace molecules: frozen out, dissociated, chemistry • angular scales are small, difficult to image – nearest regions with large samples at 140 pc, e.g. Taurus, Ophiucus, Lupus, ... • r ~ 400 AU disk • r ~ 40 AU Kuiper Belt • dr ~ 0.4 AU disk gap ~ ~ ~ SMA (e)VLA 3.0 arcsec 0.3 arcsec 0.003 arcsec CARMA (=OVRO+BIMA) HST 53 Observational Challenges • bulk of disk mass is “cold” (and dark) H2 – probed only through minor constituents – solids: thermal emission, scattered light – gas: trace species, subject to excitation and chemistry • angular scales are small, difficult to image – nearest regions with large samples at d=140 pc, e.g. Taurus, Ophiucus, Lupus, Chamaeleon, ... HST R (AU) (arcsec) outer disk 200 ~ 1.4 SMA Kuiper Belt 40 ~ 0.3 disk gap 0.4 ~ 0.003 54 Towards Nebular Chemistry • 13CO less thick and sensitive to structure SMA R=R(12CO) smaller R? depletion? 55 Selective Photodissociation • 13CO J=2-1 Rdisk << 12CO J=2-1 Rdisk Data 172 AU 110 ± 5 AU cf. DM Tau, IRAM PdBI, Dartois et al. 2003 56 Achromatic Optical Extinction 114-426 • observations at l probe particle sizes ~ O(l) • in silhouette proplyd, sub-mm ISM dust has grown, i.e. a >> l HST Throop et al. 2001 57 Infrared Spectroscopy • shape of 10 mm silicate feature depends on grain size 0.1 mm 2.0 mm van Boekel et al. 2003 58 CQ Tau Ambiguity Resolved • CQ Tau – M* ~ 1.5 M age ~ 10 Myr • 7 mm resolved – dust emission – disk models show t < 1 for r > 8 AU – for p =0.5 - 1.5, RD~100 - 300 AU, b=0.5 - 0.7 • kd ~ l-0.60.1 large grains VLA Testi et al. 2003 59 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 and large dispersion • Spitzer (e.g. FEPS): most of the action in protoplanetary disk evolution is < 5 Myr (Meyer, Hillenbrand et al.) Haisch, Lada, Lada 2001 60 Muzerolle et al. 2000 Other lcm Emission Processes • ionized jet/wind? – if Fcm dMacc/dt, then ~0.2 mJy, 103x lower than observed – spectral index 3.5-6 cm >0.3 – not likely STIS • nonthermal emission? – X-rays (Kastner et al. 1997,...) – 3.5 cm apparently variable • < 84 mJy (3s, Rucinski 1992) • 200 ± 28 mJy (Wilner et al. 2000) – plausible, but... Stelzer & Schmitt 2004 61 Disk n,T,... f(r,z): Panchromatic x-ray uv optical mid/far-ir submm cm hot gas/accr. starlight warm gas/dust cool gas/dust star dust (1% of disk mass)4’’ SMA HST TW Hya (K7) Weinberger et al. 2002 400 AU 62 Analogous Tidal Structures IRAM GG Tau Cassini: moon in Keeler Gap (zero pressure, low viscosity) GG Tau: 1.3 mm dust circumbinary disk, cleared interior Guilloteau et al. 1999 63 Molecular Clouds Disks Taurus Dark Cloud Barnard (1906) Benson & Myers 1989 900 AU Protostars Padgett et al. 1999 Dense Cores Copernicus 1543 64 Disk n,T,... f(r,z): Panchromatic x-ray uv optical hot gas/accretion mid-ir starlight far-ir submm mm cm warm gas & dust cool gas & dust star dust (1% of disk mass) 4’’ SMA HST TW Hya d=56 pc Calvet et al. 2002 65 TW Hya lcm Emission • dust disk model underpredicts 3.5 cm emission should we be interested in this difference? 66