Dust Dynamics in Debris Gaseous Disks Taku Takeuchi
Dust Dynamics in Debris Gaseous Disks Taku Takeuchi (Kobe Univ. , Japan) 1. Dynamics of Dust - gas drag - radiation 2. Estimate of Gas Mass 3. Dust Disk Structure Formed by a Planet in a Gas Disk
Gas Drag on a Dust Grain • Epstein drag law • Stopping time
Small Grains: • Due to strong gas drag, grains co-rotate with the gas, which orbits with sub. Keplerian velocity. sub-Kepler
Large Grains: • Grains orbit with the Keplerian velocity, which is faster than the gas Kepler head-wind
Orbital Decay Rate Adachi et al. 1976; Weidenschilling 1977 • As the gas mass decreases, – tmin=const. , but the size at tmin decreases • Even if the gas mass is as small as 0. 01 Mearth, grains of 1 -10 mm rapidly fall at 100 AU tmin tstop=torb
Radiation Pressure (Optically thin disk) Burns et al. 1979; Artymowicz 1988 • RP reduces the central star’s gravity reduction factor:
Direction of Grains’ Drift Takeuchi & Artymowicz 2001 • Size segregation • Dust clumping at the edge of the gas disk slower than gas fair-wind headwind faster than gas
Clumping Instability Klahr & Lin 2005 pressure • Gas temperature = Dust temperature Increase in the dust density radius
Other Radiation Effects • Poynting-Robertson drag – much smaller than gas drag • Photophoresis (Krauss & Wurm 2005) 100 AU 1 AU Force Ratio (Fph / FRP) MMSN model cold hot
Timescales • In a gas disk with Mg>Mluna, gas drag dominates the dust evolution at 100 AU
Estimate of the Gas Mass (w/o planets) • b Pic (Thébault & Augereau 2005) dust disk Gas free disk 1000 AU 100 AU Planetesimal disk
b Pic (Thébault & Augereau 2005) • upper limit: Mg<0. 4 Mearth – H 2 emission (ISO): 50 Mearth (Thi et al. 2001) – H 2 absorption (FUSE): <0. 1 Mearth (Lacavelier Des Etangs et al. 2001) – Na. I emission : 0. 1 Mearth (Brandeker et al. 2004) Gaseous disk (40 Mearth )
HD 141569 (Ardila et al. 2005) • Scattered light from b meteoroids (s~1 mm) • Mg<50 Mearth – Distribution of b meteoroids shows a spiral pattern, because it traces the distribution of planetesimals. • CO emission: Mg<60 Mearth (Zuckerman et al. 1995) Stellar flyby b meteoroids spiral wave Planetesimal disk
HR 4796 (Takeuchi & Artymowicz 2001) • Mg~4 Mearth • CII absorption: Mg<1 Mearth (Chen & Kamp 2004) gas disk Telesco et al. (2000) planetesimal disk
Gas + Planets • Resonant trapping – large grains (orbit faster than the gas): • drift inward • trapped at exterior resonances (Weidenschilling & Davis 1985) – small grains (orbit slower than the gas): • drift outward • trapped at interior resonances (Doi & Takeuchi, in prep. )
Complications by Gas Disturbances • Gap • Spiral waves • Turbulences Lubow et al. 1999
Gap • Gap opening time at j+1: j LR (Goldreich & Tremaine 1980) • Timescale to form resonant structure (Weidenschilling & Davis 1985) j+1: j j+2: j+1
Gap Opening / Resonant Trapping Timescales • Resonant trapping probably does not form prominent structure before gap opening j=10 1 MJupiter Timescale 1 Mearth j j=3 j
Gas density Grain Accumulation at the Gap Edges Bryden et al. 2000
Spiral Waves • Planet’s gravity and /or spiral waves may distort the dust rings. clumps? Lubow et al. 1999
Turbulence • Optically thin disks are probably unstable against MRI (Sano et al. 2000) • Turbulence inhibits planets from opening a gap • Can resonant trapping occur in turbulent disks? A 30 Mearth planet cannot open a gap in a turbulent disk (Nelson & Papaloizou 2004)
Type I Migration • can be neglected – Mp=30 Mearth, at 100 AU, Mg=30 Mearth, – tmig~1 Gyr (Tanaka et al. 2002)
Summary / Unresolved Questions • Gas of a lunar mass can dominate the orbital evolution of the dust • Gas drag can form structure in dust disks without any planets or companions • Gas mass can be estimated from the structure of the dust disk (if there is no planet) • What structure does a planet form in a gas disk?
- Slides: 23