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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
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
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
Outburst mechanism: general picture
GI
(Armitage et al. 2001, Zhu, Hartmann, Gammie 2009 a,b)
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)
Outburst mechanism: 2 D simulations• Compared with Observation
– Maximum mass accretion rate
– Outburst duration time
– High Ṁ disk size
– Short time scale variations
• 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
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
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.
(Evans et al. 2008)
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)
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
(Pre-)Transitional diskConstant nu
Constant alpha
TI and S curve
Σ
Tc
Cooling>heating
heating>cooling
Stable
unstable
Opacity
4.04
1
With , if the disk is convectively unstable.