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Time-Dependent Phenomena in Protoplanetary Disks
Zhaohuan Zhu
Advisor: Lee Hartmann
Collaborators: Charles Gammie(UIUC), Nuria Calvet (Umich),Catherine Espaillat(CFA), Richard Durisen, Kai Cai, Jesus Hernandez
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Introduction• “Luminosity Problem” (Kenyon et al. 1990)
– Ṁ~Mʘ /105 yrs~10-5 Mʘ yr-1
L~ ~20 Lʘ for 0.3 Mʘ, 2 Rʘ
– Observed L peaks at <0.5 Lʘ
• Solution: Infall to disk, with episodic disk accretion
*
*
2
1
R
MGM
(Evans et al 2008)
Ṁinfall~10-5 Mʘ yr-1Ṁinfall~10-5 Mʘ yr-1
quiescent outburst
Ṁ~10-8 Mʘ yr-1 Ṁ~10-4 Mʘ yr-1
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FU Ori : example of episodic accretion
(Zhu et al 2007, 2008)
0.5-1 AU
6000 K
2000 K
• Accretion disk model predicts SED, variation of spectral type and rotation with wavelength.
Accrete 10-2 Mʘ in 100 year Massive inner disk α~0.02-0.2
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Outburst mechanism: general picture
GI
(Armitage et al. 2001, Zhu, Hartmann, Gammie 2009 a,b)
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Outburst mechanism: 2 D simulations– ZEUS axisymmetric hydro-simulation of viscous fluid accretion
– With the artificial viscosity of MRI and GI and the radiative cooling
– Movie1
4 stages(Zhu et al. 2009b)
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Outburst mechanism: 2 D simulations• Compared with Observation
– Maximum mass accretion rate
– Outburst duration time
– High Ṁ disk size
– Short time scale variations
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• Longterm 1-D 2-Zone model with infall to disk
Disk long term evolution: layered picture
Fiducial model
Faster rotating core
Slower rotating core(1) (2)(3)
(Zhu et al. submitted)
(1)
MRI MRI GI
(2) (3)
Dead Zone
Ease Luminosity problemInitial core rotation important
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Compare with current observation and Predict with future obeservations
Disk long term evolution: Predictions
=10-14
=10-14
=2 X10-14
=3 X10-15
Massive dead zone within 10 AU
d=0.001
viscous
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Conclusion:• Pure TI model does not work for FU Ori outbursts
• GI+MRI model does work
• It can explain the Luminosity problem
• The disk may have a massive ‘dead zone’ which can be observed by future EVLA, ALMA observations
• Ongoing work
Azimuthal 2D to treat
self-gravity consistently
How do planets open a hole or gap in accreting disks, which can be compared with (Pre)Transitional disks.
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(Evans et al. 2008)
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FU Orionis objects: disk differential rotation
Zhu et al. 2009 b
5 µmoptical 2µm
•Support the disk accretion model•The high Ṁ disk could extend to 0.5 AU
(Close to Keplarian rotation velocity at 0.5 AU)
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FU Orionis objects: flared outer disk or envelope?
• BBW 76 & V1515 Cyg
The variety of dusty structures (flared disks for FU Ori and BBW 76; an envelope for V1515 Cyg) suggests that FU Orionis phase can be present at either early or late stages of protostellar evolution.
(Zhu et al. 2008 )
V1515 Cyg
BBW 76
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(Pre-)Transitional diskConstant nu
Constant alpha
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TI and S curve
Σ
Tc
Cooling>heating
heating>cooling
Stable
unstable
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Opacity
4.04
1
With , if the disk is convectively unstable.
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