Accretion and Variability in T Tauri Disks

James Muzerolle

T Tauri stars, ca. 1976

Rydgren, Strom, & Strom 1976: A dense, ionized

gaseous circumstellar envelope is responsible for

the continuum and line emission

Strom 1977 review suggested a way forward:

Measure photospheric absorption line depths (veiling)

Need simultaneous measures of emission lines, Balmer

continuum, veiling, and IR excess

Constrain variability timescales and look for periodicities

Investigate multiplicity

Obtain quantitative estimates of specific angular momentum and

mass outflow rates

Need more study of YY Ori phenomenon

Measure magnetic field strengths

Observe/resolve scattered light structure

Measure emission line polarization

T Tauri stars, ca. 2008

UV excess Permitted emission linesBlueshiftedabsorption

Forbidden emission

The magnetospheric accretion paradigm

H emission from magnetospheric flows

● models in good

agreement with

observed profiles

● can be used to derive

mass accretion rates

for a wide range of

young stars

Lawson et al. 2004

Gas evolution: mass accretion rates

70% 30% 5%accretor fraction:

dM/dt ~ M2

Garcia Lopez et al. 2007

Mass dependence

variability: accretion in AA Tau

● K7, 1-2 Myr-old

● P = 8.22 days

● highly-inclined disk

● optical light curve suggests

periodic occultation of star

by inner disk

Bouvier et al. 2007

● occultation events correlated with accretion

signatures

● wind, infall velocities are correlated

Bouvier et al. 2007

inclined dipole, field inflation, and disk warp?

Bouvier et al. 1999, 2003

O’Sullivan et al. 2005

Variability: dust emission probed by

Spitzer

New time-series Spitzer

observations show common

mid-IR varability in disks

● > 30% of objects

● daily – yearly timescales

● amplitudes up to 30%

Variable transition disks

Surprising wavelength dependence, timescales as short as 1 week!

● warp or corotating dynamical structure?

– may betray the presence of a stellar or low-mass companion

● variable accretion/dusty winds?

10/1/07

9/24/07

3/15/05

Artymowicz simulationVinkovic et al. 2006