Gaps, Spirals, and Azimuthal Asymmetries inProtoplanetary Disks: 	

Signposts of Planets or Not?	

董若冰 Ruobing Dong	

Hubble Fellow @ Berkeley	June. 2nd 2015, DTA Symposium, NAOJ	

1	Gaps, Spirals, and Asymmetries in Protoplanetary Disks: 
Signposts of Planets or Not?	

• YES observed gaps are consistent
with a planet origin	• UNCLEAR whether spiral arms
and azimuthal asymmetries arecaused by planets or not	• Alternatives exist, and may do abetter job than planets in
explaining some observations	

Gravitational Instability		Vortex	

Disk-star interaction	

2

Protoplanetary Disks: The Birthplaces of Planets	

A young star	

Hundreds of AU	

Dust and gas	3

Dissipation of Primordial Gas and Dust 
A Few Million Years	

Gas giants and	embryos of terrestrial planets	

Debris Disks	4Long Term Evolution…	

A Mature Planetary System Around a Main Sequence Star	

5

Protoplanetary Disk	

Debris Disk	

A few Myr	Main Sequence Star	

Billion years	

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Directly look for planets in protoplanetary disks?	

Radial Velocity	Transit	Direct Imaging	Where are the lions?	

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What Do Planets Do in Disks?	

Perturb the Disk and Excite Features	

Gap Opening	Spiral Density Wave	

F. Masset 	Observations of Disk Features in Planet Formation Regions	• Nearby star forming region: ~140 pc (e.g. Taurus)	

• Planet-induced features at 10s of AU: ~1 – 10 AU	

• 1 AU at 140 pc: ~0.007”	

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High Resolution Disk Observations	

λ=D= 0.01"− 0.1"8m class mirrors	

with AO systems	

~1 um – polarized scattered light

Subaru/HiCIAO/SEEDS

10 km baseline radio
interferometers	 Laura’s talk	~1 mm – thermal / lines emissions

Gemini/GPI

Atacama Large mm/sub-mm Array (ALMA)	

VLT//SPHERE

Karl G. Jansky Very Large Array (JVLA)	

Nobuhiko’s talk	11

Observed Features in Protoplanetary Disks	

I. Giant Gaps in Transitional Disks	

II. Multiple Separated Gaps in HL Tau	III. Spiral Arms	

IV. Large Scale Azimuthal Asymmetries	

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Features in Disks I: Giant Gaps in Transitional Disks	

Wavelength Dependent Gap Sizes 	

USco J1604	

HD142527	

SAO 206462	

2.2 um	

1.6 um	NIR	

140AU	

Mayama+12 (Subaru)	

Avenhaus+14 (VLT)	

Garufi+13 (VLT)	

mm	0.5”, 70AU	

Zhang + 14 (ALMA)	

Casassus+13, Fukagawa+14 (ALMA)	

Pérez+14 (ALMA)	

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Features in Disks I: Giant Gaps in Transitional Disks	

The “Missing Cavity” at NIR	Observations of SR 21	

SMA 0.88 mm	

Physical Disk Structure	~mm-sized dust	

Andrews + 2011	

SEEDS H-band 1.6 um	

Follette+ 2013	~(sub-)um-sized dust	Dong, Rafikov, Zhu + 2012 	

Zhu, Nelson, Dong+ 2012	

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Features in Disks II: Multiple Separated Gaps	Eiji’s talk	

HL Tau1.3 mm continuum
Brogan, Pérez +15• Age: ≤ 1-2 Myr	• Mdisk/Mstar: ~ 0.1-0.25 	

(Kwon+11)

30 AU15

Features in Disks III: Spiral Arms	

SAO 206462

MWC 758

Subaru H bandSubaru H band

Muto+12

Grady+1316

Features in Disks IV: Large Scale Azimuthal Asymmetries	

contrast 1.5:1	

ALMA mmcontinuum	

70 AU	

SAO 206462, Pérez+14	

contrast 130:1	

contrast 1.9:1	

70 AU	SR 21, Pérez +14	

contrast 30:1	

140 AU	IRS 48, van der Marel+13	

HD 142527, Fukagawa+14, Casassus+13	

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Observations	

Theory	Planets	

F. Masset	

Alternatives	

Gravitational Instability	

Vortex	Disk-star interaction	

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Disk Feature Modeling	• General work flow	• Features induced by planets: gaps and densitywaves	• Features induced by alternative mechanisms:density waves and large scale asymmetries.	

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Disk Feature ModelingGeneral Workflow	

Step I	

Step II	

Step III	

Hydro simulations tocalculate disk structuresinduced by variousmechanisms	

Radiative transfer simulations
to produce synthetic images	

Post processing of modelimages	

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An Example: Gaps Opened by 3 Planets
2D 2 Fluid (gas+particle) Simulation	

••
•
•
•

Step I	

Step II	

Step III	

2D 2 Fluid (gas+particle)
simulations to calculate
disk structure	

3D Monte Carlo radiativetransfer simulations toproduce model images	

post processing ofsynthetic model images	

sub-um grains	

NIR	NIR	

mm grains	

mm continuum	

mm continuum	

3x0.2 MJ planets
12, 30, 65 AU	

α (viscosity)
0.001	

Initial disk mass0.2 M¤
Evolution time
0.2 Myr	mm beam size
0.035”	

Dong, Zhu, & Whitney 2014	

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Planet-Induced Multiple Gaps	Models	Observations	

3x0.2 MJ planets; Mdisk/Mstar=0.2; 0.2 Myr	

Age: <1 Myr; Mdisk/Mstar: ~ 0.25 (Kwon+11)		

mm continuum	Dong, Zhu, & Whitney 2014	

HL TauBrogan, Pérez+15
Kazuhiro’s talk, Shu-ichiro’s talk	22

Planet-Induced Giant Gaps	Models	••Observations	The wavelength dependent gap sizes	

A model with four 2MJ planets	

NIR	mm	Dong, Zhu, & Whitney 2014, Pinilla +12, Zhu, Nelson, Dong + 12, de Juan Ovelar + 13	23

Planet-Induced Giant Gaps	Models	•Models withmultiple giant
planets	

Observations	

•NIR gap contrast	

Gap contrast 3.5	Gap contrast ~3.5	

Gap contrast ~3.6	

Four 1 MJ planets	

Hashimoto, Dong+12	

Mayama…Dong+12	

Gap contrast 6.0	HR 8799, Marois et al.	

Four 2 MJ planets	

Gap contrast ~3.3	

Gap contrast ~4.2	

Garufi+13	

Avenhaus+14	24Dong, Zhu, & Whitney 2014	

HR 8799,

Planet-Induced Density Waves	

Models	Waves too weak	 Observations	Surface Density	

MWC 758

Hydro models	

2D Fargo	Density enhancement at thewaves: ~30%	

Muto+12	

SAO 206462

Full resolution NIR image	 Convolved NIR image	

Juhasz+15	

Grady+13	25

Planet-Induced Density Waves	

Models	Waves too weak	 Observations	Surface Density	

Parameterized wave 	Density enhancement at thewave: 2.5	MWC 758

Convolved NIR image	Muto+12	

SAO 206462

This is ~1 order of magnitude
higher than what a planet can do	Juhasz+15	

Grady+13	26

Alternatives: Gravitational Instability	

(Shantanu’s talk)	

Models	Hydro: 3D SPH (Lodato &Rice)	

••••Too many arms	

Low contrast	

Observations	

MWC 758

Surface Density	

Mdisk/Mstar= 0.25	

Disk Size: 300 AU	

Isolated disk	

Slow cooling:tcool=7.5/Ωorbit(fragmentation attcool<3/Ωorbit )	

Muto+12	

SAO 206462

NIR image	

Marginally unstable,narm~5, moderate density
contrast (a factor of afew)	

Grady+13	

Dipierro+15	

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Alternatives: Gravitational Instability	

(Shantanu’s talk)	

Models	Fragmentation andclump formation	

Surface Density	

Observations	

MWC 758

Hydro: 2+1D grid code(Vorobyov & Basu)	

••••Mdisk/Mstar= 0.25-1	

Disk Size: ~500 AU	

Cooling is handled bydiffusion approximation 	

Disk surrounded by anenvelope, material in-fallongoing.	

Muto+12	

SAO 206462

NIR image	

Strongly unstable, hugedensity contrast (up to~100), clump forming	

Grady+13	

Dong, Vorobyov +15, in prep.	

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Large Scale Azimuthal Asymmetries: Options	

Options	

Assumption: Optically thin emission

Fv ∝ v × κ v × Td × Σ d2

Observations	1.5	

van der Marelκ v Dust opacity	

Td Dust temperature	

1.9	Pérez+14	

130	30	Σ d Dust surface density	

van der Marel+13	

Fukagawa+14, Casassus+13	29

Large Scale Asymmetries: Theories	

Theories	

Observations	mm image	

mm dust	Gas	Vortex at gap edges	

Zhu & Stone 2014, Lyra & Lin 13	Gas	mm dust	HD 142527, Fukagawa+14, Casassus+13	

•••Gravitational global mode in disks (disk-star interation)	

Mittal & Chiang 2015	

Pattern Size (radial)	

Pattern Speed	Wavelength Dependent PatternLocation	

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Directly Search for Planets in Protoplanetary Disks?
Yes it can be done, but it is difficult.	

LkCa 15b, Kraus & Ireland 2012	

HD 142527b (stellar mass companion) 	

Close et al. 2014	

HD 169142b	

Reggiani et al. 2014	

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More massive planets are needed to open giant gaps withmultiple planets than with a single planet	Surface density of gas in a system with	

One planet	

Duffell & Dong 2015	

Two planets	

Three planets	

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Gaps, Spirals, and Azimuthal Asymmetries in Protoplanetary Disks: 

Signposts of Planets or Not?	

• YES observed gaps are consistentwith a planet origin	• UNCLEAR whether spiral armsand azimuthal asymmetries arecaused by planets or not	

• Alternatives exist, and may do a
better job than planets in somecases	

Gravitational Instability	• Transitional disks may be ourbest bet to directly see planets.		

Vortex	Disk-star interaction	

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