Presentation on theme: "Cumber01.ppt 30.5.2001 Thomas Henning Max-Planck-Institut für Astronomie, Heidelberg Protoplanetary Accretion Disks From 10 arcsec to 10 -3 arcsec HST."— Presentation transcript:
Cumber01.ppt 30.5.2001 Thomas Henning Max-Planck-Institut für Astronomie, Heidelberg Protoplanetary Accretion Disks From 10 arcsec to 10 -3 arcsec HST STIS – Grady et al. 2001 HD 100 546
NIR/Mid-IR thermal dust (VLTI: Midi, Amber) Scattered Light in Optical and NIR (opt. thick) mm / submm thermal dust emission (opt. thin) Optically thick CO lines thin lines Domain sampled in current images at 150 pc 0 - 200 200 ~ 500~ 100~ 50~ 1 Vertical scale near the star Approximate radius r (AU) Approximate H(r) at 500 AU (AU) Flaring? Planetesimals?Acc. Rate ~10 - 8 M /yr Accretion columns (broad emission lines: Hα, etc) Accretion shock Stellar magnetosphere Accretion disk ~ Kuiper Belt Passive reprocessing disk Wind Cumber03.ppt 30.05.2001 Adapted from A. Dutrey
Fundamental Questions How is angular momentum transported in disks (Self-gravity, turbulence – MRI or global baroclinic instability)? How do planets form in disks? Is the accretion process important for star formation (IMF)? Klahr & Bodenheimer (2003)
Open Issues Geometrical structure (inner+outer edge, vertical structure, flaring, warps, gaps,...) Temperature and density distribution Accretion rate – time variation Chemistry in disks and evidence for grain growth Transition from optically thick to optically thin disks Disk structure vs. nature of central star
How do we know that disks exist? Inference Theory of SEDs Infrared emission Millimetre dust continuum emission Polarization of light Jets Proof HST images Millimetre maps (interferometry) Adaptive optics images Images in the thermal infrared
Speckle and AO-assisted Observations from the ground (scattered light, extinction lanes) IRN Cha Ageorges et al. 1996 HV Tau C Stapelfeldt et al. 2003 HST (coronographic) images: STIS, NICMOS, WFPC (scattered light, extinction lanes)
Thermal infrared observations Millimetre continuum and line data (dust emission – optically thin; gas emission – mostly optically thick) HR 4796 A – Telesco et al. 2000 CB 26 - Launhardt & Sargent 2001
Geometrically thin disks (Adams et al. 1988) Temperatures correspond to unique radii T d (r) = 1000 K (r/1AU) -3/4 Each frequency traces distinct temperatures S = cos B (T d (r) ) [1- exp (- ( ))] 2 r dr/D 2 ( ) <<1 S ~ ( ) M disk (Rayleigh-Jeans limit) ( ) >>1 S ~ 4/3 (Reprocessing or accretion) SEDs from a geometrically thin simple disk almost never fit observed SEDs Industry of more sophisticated models
Silicate Emission in T Tauri Disks Natta, Meyer, & Beckwith, ApJ, 2000.
SEDs of T Tauri Stars: A Consequence of Inner Holes? Dullemond et al. 2001
The GM Aurigae Discussion Analysis of SED (Rice et al. 2003) Inner hole created by a ~ 2 Mj planet orbiting at 2.5 AU in a disc with mass 0.047 M sun and radius 300 AU But: SED contains limited spatial information (geometry / opacity problem) Boss & Yorke 1993, Steinacker & Henning 2003 Other mechanisms: Disc wind caused by photoevaporation (Clarke et al. 2001) Higher temperature due to accretion shock front (dAlessio et al. 2003) Destruction of grains by non-thermal processes (Lenzini et al. 1995, Finocchi et al. 1997)
Structure in Disks Structure in disks older than 2 Myr is common. Seen in T Tauri and Herbig Ae stars. In some cases associated with dynamical clearing DL Tau DM Tau HD 141569A, Mouillet et al. 2000 HR 4796A, Schneider et al. 2001 HD 100546
Where Are Envelopes Seen? Associated with single, isolated stars. All objects with large-scale nebulosity have distinctive mid-IR spectra. While the optical depths appear to drop with age, these large-scale nebulosities are seen over the entire PMS lifetime of intermediate-mass stars. SU AurHD 100546CQ Tau
Properties of T Tauri Disks: What is Known? 50% of the objects have disks M disk << M * in case of T Tauri stars (typically: M disk 10 -2 M sun ) Disk diameters: 50-200 AU Disk lifetime: 10 6 yr Accretion rates: 10 -9... 10 -7 M sun yr -1
Disk Structure Inferred from IR Near-IT traces emission r < 0.1 AU Some evidence for inner holes in accretion disks Mid-IR spectro-photometry from KAO/ISO/ground: Indicates optically thin hot dust r < AU Far-IR observations of outer disk 1-5 AU Warm grains in disk atmosphere?
Factors Influencing Disk Evolution Stellar mass: Do high mass stars lose disks quicker? Close companions: dynamical clearing of gaps (Jensen et al. 1995; 1997; Meyer et al. 1997b; Ghez et al. 1997; Prato et al. 1999; White et al. 2001). Formation environment: cluster versus isolated star formation
Growth Processes in Disks 1 mm Dust grains 0.1 – 1 mm - Gas-dust interactions - Sticking collisions in multi-particle systems 1-10 km Planetesimals ~ 10 km - Gravitational interaction (Decoupling from the gas) - Agglomeration by pairwise collisions - Explosive growth of the largest planetesimals in the accretion zone 10 3 km Protoplanets – dynamically isolated - Accumulation of solid material - Accumulation of H 2 und He by massive protoplanets Cumber12.ppt 5.6.2010
Grain Growth Some evidence for grain growth from mm observations and polarization studies in the IR Micron- to centimetre-sized grains and agglomerates stick at the typical relative velocities occurring in protoplanetary disks Grains couple with f m/ s g v th to the gas Agglomerates produced by Brownian motion (and most likely by other velocity fields) have open structure: f R 0.2 Crystalline silicates exist in protoplanetary disks Cumber05.ppt 30.5.2001
Evidence for grain growth Decrease in the NIR emission – TTS more than 3 million years old no longer have disks dominated by micron-sized grains (Dutkevich 1995) Flatter SEDs at millimetre wavelengths (Mannings and Emerson 1994, Koerner et al. 1995) Gray opacities in the dense core region around HL Tau from detailed RT modeling (Menshchikov & Henning 1998) Formation of gaps (Koerner et al. 1998: HR 4796) Geometrically thin disks (Alessio et al. 2001) Radiative transfer modeling of Herbig Ae/Be stars (Bouwman et al. 2000, Meeus et al. 2001) Wavelength-dependent disk size (Throop et al. 2001) ??? Cumber08.ppt 1.6.2001
Dust Opacity: Effects of Size and Composition shown at R=100 (Henning et al. 2000)
Images of edge-on disks at = 0.814 m for dust mixtures Cumber11.ppt 5.6.2001 DAlessio et al. (2001)
Time Scales For Grain Evolution t 5 10 6 yr (from infrared excess emission) (1) Dust grains have been thoroughly removed from circumstellar disks. (2) Grains have been evolved into larger bodies (reduced effective radiating surface). (3) (Replenishment of grains in disks around Vega-type stars (t 100Myr) by collisional shattering of lager bodies) Cumber04.ppt 30.5.2001
The Transition between Thick & Thin: Primordial Disks: –opacity dominated by primordial grains. Debris Disks: –Opacity dominated by grains produced through collisions of planetesimals. How can you tell the difference? –Absence of gas (Gas/Dust < 0.1) argues for short dust lifetimes (blow-out/P-R drag). – Dust processing through mineralogy?
Disk geometries proposed for Herbig Ae/Be stars Group I with FIR excess Group II no FIR excess flaring disk self-shadowing disk The special feature of these models is the puffed-up hot inner rim of the disk Dullemond, Dominik & Natta 2001 Dominik, Dullemond, Waters & Walch 2003
Detecting Planets in Protoplanetary Disks Radial density profile in the midplane (M = 1 Mj at 5.2 AU) Normalized visibilities at = 10 m, d = 140 pc (0° - face on, 60°) Wolf et al. (2002), Steinacker & Henning (2003)
Conclusions Brandner et al. (2000) Goal – Imaging of disks with infrared and millimetre interferometry (Evidence for disk structure and grain growth scarce) Fundamental physical processes not understood (Complicated interplay between microphysics and MHD)
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