Planet and Gaps in the disk Hwihyun Kim Feb. 8 2006

PAPERS Forrest, W. J., et al., 2004, ApJS, 154, 443 “Mid-IR spectroscopy of disks around classical T Tauri stars” 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 Recent discovery of CoKu Tau/4 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 presence of planet Outer disk is still accreting Inner hole is left after the formation of a planet Associated with planet formation in the disks surrounding young stars 2. suggests that planet formation can take place quite early stage of evolution 3. Ability to open a gap that block the mass flow to smaller radii 4. Because massive planet can not be formed at small radii from the star

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 1.Viscosity : resistance of a fluid, or resistance to pouring 2. Reynolds number : dimensionless number, smoothness of the flow of fluid, ratio of inertial force to viscous force Laminar flow : low Re, high viscosity / Turbulent flow : high Re, low viscous (Saturn ring picture) 3. Viscous timescale : high viscous material (low Re) can fall inward quickly

Wavemaker moon Low viscous material-----high Reynolds number (turbulent flow)

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 accrete 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 τp < τν < τage 1. Outer disk material cannot be accreted across the planet’s orbital radius because there is the transfer of orbital angular momentum from the planet to the disk.

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 To open a gap, a planet must be massive because the spiral density waves(dissipated in the disk) should overcome the inward flow(due to viscosity).

PLANET MIGRATION Interaction between the planet and surrounding disk To maintain the gap, Balance of the torque density from spiral waves and inward torque from viscous accretion Mp < Md : outward migration CoKu Tau/4 : lack of significant migration Migration is caused by the interaction. Interaction leads a transfer of ang. Mom. Migration may occur after opening a gap Spiral waves from the different resonances No migration : still resides a large distance from the star. Sufficient mass has not accumulated in the disk edge.

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 early in the evolution of protostellar systems

SPECTRUM Excess of emission 5-8 μm : characteristic of accretion disks around young stars Beyond 8 μm : emission from small silicate grains Spectrum from Spitzer observation shows the excess of emission

FM Tau vs. CoKu Tau 4 FM Tau CoKu Tau 4 Has accretion disk Actively accreting CoKu Tau 4 Decrease in emission in short-wave IR Dusty disk with a gap at 10 AU CoKu Tau is unique. No excess emission from the accretion disk in 5-8 micron. Below the extrapolated stellar continuum Broad peak 10-12 and small dip 12.5 then rapid rise. This emission is from the heated dust surrounding the star Low excess means that there are very few small grains closer to the star ------gap!!

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 Before we see the CoKu Tau 4 ‘s disk structure, more about the gap.

DISK MORPHOLOGY Lindblad resonances This is the predicted disk morphology with a planet mass 0.1Mj. Because of the proximity of the planet and disk, high-order spiral density waves are driven by the planet at Linblad resonances. If these waves are constructive interference, the result is a spiral pattern rotating with the planet.

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 high Re : viscous time scale is long Large planet mass : no migration to the outer disk

INNER HOLES IN DISKS Observation Simulation Detected through the study of SEDs Confirmed by direct images (scattered light image) CO line emission in T Tauri stars Simulation Combination of 2D hydrodynamics simulation and 3D Monte Carlo radiative transfer code 3D simulation : because the gap is vertically extended They can make the planetary gap with vertically extended density.

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 Created using 10^8 photons The gap width (FWHM) is about 1 AU The images show a 7 AU × 7 AU region. Edge of the disk to the inner hole is brighter than outer disk on both with a gap and w/o a gap.

SURFACE BRIGHTNESS PROFILE Bright bump : 4 times larger than the emission from the smooth disk This is caused by the direct illumination of the outer wall of the gap because the stellar photon can not be absorbed anymore by the disk material. The photon from the star hit the wall of outer gap. 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) Small-hole : shallow bump(emission deficit) -------large-hole : deep bump & excess of emission Gap doesn’t change the bolometric IR flux Focus on the right-bottom 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

Planets sweep up the material around them and clean up the gaps. When the accretion stops, the disk is dissipated and creates a large central hole! 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 the 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 vertical disk wall Back illumination heats the outer gap wall (emission excess and deficit in SED)