1. Accretion and Variability in T Tauri Disks James Muzerolle

2. T Tauri stars, ca. 1976 Rydgren, Strom, & Strom 1976: A dense, ionized gaseous circumstellar envelope is responsible for the continuum and line emission

3. 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

4. T Tauri stars, ca. 2008

5. UV excess Permitted emission lines Blueshifted absorption Forbidden emission The magnetospheric accretion paradigm

6. 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

7. Kurosawa et al. 2006

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

9. dM/dt ~ M 2 Garcia Lopez et al. 2007 Mass dependence

10. 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

11. occultation events correlated with accretion signatures wind, infall velocities are correlated Bouvier et al. 2007

12. inclined dipole, field inflation, and disk warp? Bouvier et al. 1999, 2003 OSullivan et al. 2005

13. 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%

14. 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