Accretion and Variability in T Tauri Disks James Muzerolle

T Tauri stars, ca 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 lines Blueshifted absorption 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

Kurosawa et al. 2006

Gas evolution: mass accretion rates 70%30%5%accretor fraction:

dM/dt ~ M 2 Garcia Lopez et al 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 OSullivan 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 simulation Vinkovic et al. 2006