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S.Walch, A.Burkert, T.Naab Munich University Observatory

Formation & evolution of protostellar disks around low-mass stars. S.Walch, A.Burkert, T.Naab Munich University Observatory. Initial Conditions. Density: Bonnor-Ebert Sphere Central density:  max =10 -18 g/cm³ Temperature: T = 20K Cut-off radius:  BE  = 6.9  0.1pc

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S.Walch, A.Burkert, T.Naab Munich University Observatory

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  1. Formation & evolution of protostellar disksaround low-mass stars S.Walch, A.Burkert, T.Naab Munich University Observatory From protostellar cores to disk galaxies - Zurich - 09/2007

  2. Initial Conditions • Density: Bonnor-Ebert Sphere • Central density:max =10-18 g/cm³ • Temperature:T = 20K • Cut-off radius:BE = 6.90.1pc • Total mass of the sphere: MBE 5.5Msun • EOS: • Adiabatic ( =1.4 for H2) + Molecular line cooling: Neufeld et al., (1995): Mostly H2, CO, H2O, HCl, O2  = Etherm/Epot   0.1 From protostellar cores to disk galaxies - Zurich - 09/2007

  3. Initial Conditions • Velocity & Angular Momentum: • Thermal line-widths • Velocity gradient maps (e.g. Caselli 2002) From protostellar cores to disk galaxies - Zurich - 09/2007

  4. Initial Conditions • Velocity & Angular Momentum: Caused by: • Overall core rotation? From galactic differential rotation; clump-clump collisions? • Sub-/Transonic Turbulence?(Burkert & Bodenheimer 2000) Random Gaussian Velocity Fields; P(k) kn , n=-3..-4 • Can turbulence account for net rotation? • Reproduces Line-Width - Size relationship (Larson 1981): () q (n=-3-2q), q=0.25..0.75 (e.g. Fuller & Myers 1992) (Kolmogorov: q=0.33, n= - 11/3) • Reproduces projected rotational properties of cores  = Erot/Epot   0.01 From protostellar cores to disk galaxies - Zurich - 09/2007

  5. Numerical Issues VINE-Code: (Wetzstein et al.) • MPI-Parallel N-Body + SPH Code • Resolution: • 430 000 Particles • -> Particle Mass: 1.28·10-5M • -> Min. resolvable Jeans Mass: 1.28·10-3M • -> Switch in EOS => Mjeans always resolved! • Minimum Smoothing Length: hmin = 2AU • BoundaryConditions: • PeriodicinHydro • IsolatedinGravity From protostellar cores to disk galaxies - Zurich - 09/2007

  6. Rigid rotation vs. turbulence Rigidly rotating core: =6•10-14 s-1 => j=1021 cm2s-1 Turbulent core: j=2.7•1021 cm2s-1 From protostellar cores to disk galaxies - Zurich - 09/2007

  7. Rigid rotation vs. turbulence From protostellar cores to disk galaxies - Zurich - 09/2007

  8. Rigid rotation vs. turbulence From protostellar cores to disk galaxies - Zurich - 09/2007

  9. Global core structure 0.1 pc across z From protostellar cores to disk galaxies - Zurich - 09/2007

  10. Global core structure 104 AU across From protostellar cores to disk galaxies - Zurich - 09/2007 z

  11. Global core structure 2000 AU across From protostellar cores to disk galaxies - Zurich - 09/2007 z

  12. Origin of spiral arms? From protostellar cores to disk galaxies - Zurich - 09/2007

  13. Conclusions • SBR: Nice big disks, which grow constantly in size & mass • Filamentary & elongated (prolate) global core structure • Disk sizes are in agreement with later observations • Average Accretion Rates in “Class 0“ stage: • Solid Body: 6.4 ·10-5 Msun/yr • Hb17: 2.3 ·10-5 Msun/yr • With turbulence, irregular infall, accretion is dynamically very complicated: Disks are warped and tilted • No Fragmentation: Global gravitational torques cause spiral structure • Wide binaries may form due to turbulence in the core - even in Bonnor-Ebert sphere! From protostellar cores to disk galaxies - Zurich - 09/2007

  14. Outlook • Predict observables (ALMA, SCUBA, Spitzer) Bridge gap ! When can we first observe young protostars? • Parameter study: Fragmentation & Characteristic disk parameters -> Brown Dwarf formation? In core / in disk? -> Gas giant planet formation? Do disks become massive enough? Toomre unstable? From protostellar cores to disk galaxies - Zurich - 09/2007

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