Planet and Gaps in the disk

Hwihyun KimFeb. 8 2006

PAPERS

• Forrest, W. J., et al., 2004, ApJS, 154, 443– “Mid-IR spectroscopy of disks around classical T Tauri star

s”

• Quillen, A. C., et al., 2004, ApJL, 612, L137– “On the planet and the disk of CoKu Tauri/4”

• Varnière, P., et al., 2006, ApJL, 637, L125– “Observational properties of protoplanetary disk gaps”

INTRODUCTION

• Debate– About the nature and time-scales

• Recent discovery of CoKu Tau/4– Young star containing a 10 AU hole (Forrest et al.,

2004) – Link between the inner hole in the disk and the pre

sence of planet– Outer disk is still accreting– Inner hole is left after the formation of a planet

PARAMETERS• Disk viscosity (ν ) :

• Reynolds number (Re) :

• Timescale for the inward accretion (τν) :

– α : viscosity parameter– cs : sound speed– h : scale height– Ω : angular rotation rate– r : radius of orbit

sc h 2Re /r

Re / 2orb :

Wavemaker moon

CLEARING THE INNER DISK

• Planet in the stellar disk forms a hole– Outer disk material is prevented from the accretion

• Presence of the hole– Implies that the inner disk material has time to accret

e onto the star

• For low α and low h – Low viscosity, so high Re : higher τν

– Inner disk has no time to accrete onto the star

• Should be τ p < τν < τ age

GAP OPENING

• Inner disk will begin accreting after a newly formed planet opens a gap

• To open a gap...– Sufficiently massive : q > 40 Re-1

– q = Mp/ M*– Mp of CoKu Tau/4 > 0.1 Mj

PLANET MIGRATION

• Interaction between the planet and surrounding disk

• To maintain the gap, – Balance of the torque density from spiral waves and in

ward torque from viscous accretion

• Mp < Md : outward migration

• CoKu Tau/4 : lack of significant migration

CoKu Tauri/4• Location : Taurus-Auriga cloud• Spectral Type : M1.5 / Mass : 0.5 M⊙

• Luminosity : 0.6 L ⊙ / Distance : 140 pc

• Very special young star– Gap with radius 10 AU– Inner wall with half-height 2 AU

• Gas planet with age < 1 Myr– Suggests that the planet formation can take place quite ea

rly in the evolution of protostellar systems

SPECTRUM

• Excess of emission – 5-8 μ m : characteristic

of accretion disks around young stars

– Beyond 8 μ m : emission from small silicate grains

FM Tau vs. CoKu Tau 4

• FM Tau – Has accretion disk– Actively accreting

• CoKu Tau 4– Decrease in emission in

short-wave IR– Dusty disk with a gap at

10 AU

HOW THE GAP CAN EXIT

• Interactions with the outer disk– Lindblad Resonances → Angular momentum

• Constraints on the mass– Angular momentum → inward migration– MP > M disk edge → no migration

– MP ≤ M disk edge → migration

DISK MORPHOLOGY

• Lindblad resonances

DISK MORPHOLOGY• Proximity of the planet to the disk edge

– More than one resonance– Multiple spiral density waves can be driven at these resonances

• Spiral pattern depends on– Scale height and disk temperature (i.e. Smaller height and cooler disk : tightly

wound)

• High Reynolds number or large planet mass– Disk edge would be far from the planet

INNER HOLES IN DISKS

• Observation– Detected through the study of SEDs– Confirmed by direct images (scattered light ima

ge)– CO line emission in T Tauri stars

• Simulation– Combination of 2D hydrodynamics simulation a

nd 3D Monte Carlo radiative transfer code

SCATTERED LIGHT IMAGE

The top panels : log of the disk surface brightness viewed at an inclination of i = 5

The bottom panels : disks viewed at i = 70

On the left : no gap in the disk

On the right : a gap created by a 2MJ planet at 1 AU

SURFACE BRIGHTNESS PROFILE

• Comparison between the two disks • * : no planet + : 2Mj planet at 1AU• Decrease near the planet and bright bump at the outer edge of

the gap

SPECTRAL ENERGY DISTRIBUTION

• Current instruments – Insufficient spatial resolution– only detect gaps in the outer regions

• SEDs– Indirect detection of planetary gaps– BUT, no unique features

SEDs

• IR SEDs– Left : small-hole (r=0.07 AU)– Right : large-hole (r=1 AU)– Top : ISM dust– Bottom : HH 30 dust (high portion of big grains)– Solid line : with a gap– Dotted line : no gap

http://www.spitzer.caltech.edu/Media/releases/ssc2004-08/ssc2004-

08v3.shtml

SUMMARY

• Recent discovery by Forrest et al.(2004)– Young stellar system with a planet (CoKu Tau 4)– Inner disk has accreted within a time equivalent to the

age of the star(1 Myr)– Planet could be accreting material and interact with th

e disk by driving waves into the disk from resonances

• Simulation of the inner hole in the disk– Direct back illumination by stellar photons of the vertic

al disk wall– Back illumination heats the outer gap wall (emission e

xcess and deficit in SED)