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.