1. Probing the Conditions for Planet Formation in Inner Protoplanetary Disks James Muzerolle

2. Motivation: diversity of planetary systems wide range of system architectures: periods, masses, eccentricities – unexpected hot Jupiters, multiple planets in resonances wide range of parent star properties – all masses yet surveyed, some metallictiy dependence Is the solar system atypical?

3. Disks: planetary birthplaces How do planets form from circumstellar disks? how do the gas and dust components of disks evolve? what is the range of disk lifetimes? is disk dissipation directly related to planet formation? focus on the inner ~5 AU of protoplanetary disks: accretion indicators to probe gas content at star-disk interface infrared continuum excess at <24 micron to probe warm dust in the planet formation region of disks identify and characterize disks in the process of being cleared out

4. Context: the star formation paradigm

5. Evolution: from primordial protoplanetary accretion disks To planetary systems with debris disks Fomalhaut debris disk, HST/ACS HD 141569 transition disk, HST/ACS

6. Disk accretion in a nutshell flat disk in keplerian rotation gas accretes inward, angular momentum transferred outward disk structure for alpha disk model: – dM/dt R -3/4 dM/dt provides a crucial constraint!

7. Magnetospheric accretion ballistic motion along magnetic field lines –V infall ~ (GM * /R * ) 1/2 most disk material accreted onto star, ~10% lost in wind –emission produced in the flow can be used to trace disk mass accretion rate V infall

8. determine dM/dt as a function of mass & age to trace the evolution of gas in accretion disks Standard method: UV excess from the accretion shock L UV ~ L acc ~ GM * /R * dM/dt – limited to low extinction, low mass stars Alternate method: emission line profiles from magnetospheric accretion flows – depends on radiative transfer modeling

9. Radiation from circumstellar disks geometrically thin, optically thick flat disk heating from irradiation, viscous dissipation F = F * + F visc ~T * 4 R * 3 ~dM/dt T ~ R -3/4 => F ~ -4/3 most disks are flared more flux at mid- to far-IR, > -4/3

10. Flared vs. settling Dust & gas well-mixed, vertical hydrostatic equilibrium T ~ R -3/4, H ~ R 9/8 flared surface Grain growth – settling of large grains to midplane, reduced opactiy in irradiation surface – decrease MIR flux

11. Tools Radiative transfer modeling Gas emission line profiles from accretion flows SED models of disk structure Optical/infrared observation Optical photometry & spectroscopy – ages, masses, accretion activity of young stars Infrared imaging & spectroscopy – dust emission from circumstellar disks

12. Protoplanetary disk evolution What mechanism(s) drive disk evolution and dissipation? Is the dust and gas dissipation coupled? Is disk clearing radially dependent? Are there dependences on stellar mass, age, environment? Can we see indirect evidence of planet formation?

13. First evidence for dust disk evolution Hillenbrand 2003 NIR excess: R~0.1 AU

14. Gas evolution: mass accretion rates viscous disk similarity solutions 70%30%5%accretor fraction:

15. Probing cooler dust - Spitzer MIR excess (< 10 m) R<~0.5 AU Muzerolle et al. 2008

16. Dust evolution via grain growth & settling? Spectral slope probing dust at r < 0.5 AU decrease in mean value at older ages – precursor to dissipation? large dispersion at any given age! Hernandez et al. 2007

17. Flaherty & Muzerolle 2008 Disks in embedded clusters: NGC 2068/2071 t~1-2 Myr ~75% disk fraction some disks with smaller excess at 3.6-8 and 8-24 microns correlation of accretion activity with SED shape? two transition disks (2% of total disk population)

18. NGC 2068/2071

19. NASA/JPL-Caltech/T. Pyle (SSC) disk dissipation: transition disks Understanding how protoplanetary disks dissipate: – What are the mechanisms for primordial disk dissipation? – What are the time scales? Does the gas go away at the same time as the dust? – Do disks clear from the inside-out? – Is there a dependence on mass or age? Transition disks: where the clearing process has begun

20. Taurus dust holes ~2-24 AU 2/3 still accreting gas inner optically thin disk in GM Aur CoKu Tau/4 is a circumbinary disk! (Ireland & Kraus 2008) Calvet et al. 2005 CoKu Tau/4 DAlessio et al. 2005

21. Spitzer cluster survey Transition disks identified via spectral slopes Muzerolle et al. 2008

22. Spitzer statistics Transition phase appears even at t <~ 1Myr ~1% of stars fast? 10 4 – 10 5 yrs fraction increases with age ~5-15% at 3-10 Myr span full range of stellar spectral types, but less common in M stars? mix of accretors & non-accretors Muzerolle et al. 2008

23. Lada et al. 2006 Carpenter et al. 2006 A0 G0K0 M0 Mass-dependent disk dissipation Upper Sco

24. brown dwarf transition disk M6.5, M~0.075 Msun not accreting? inner hole size ~0.5-1 AU Muzerolle et al. (2006)

25. Inner disk clearing mechanisms photoevaporation dust grain growth giant planet formation binary dynamics?? Quillen et al. 2004

26. Najita, Strom, & Muzerolle 2007 giant planet formation? photoevaporation? demographics Taurus disk masses, accretion rates: transition disks occupy unique loci

27. A new wrinkle: variability Disks are not perfect axisymmetric structures! Accretion is known to be non-steady…. New time-series Spitzer observations show common mid-IR varability in YSOs > 30% of objects Daily – yearly timescales Amplitudes up to 1 mag 6 months3 years

28. Variable transition disks Surprising wavelength dependence, timescales as short as 1 week! warp or corotating dynamical structure? – may betray the presence of a giant planet or brown dwarf companion variable accretion/dusty winds? 10/1/07 9/24/07 3/15/05 Artymowicz simulation Vinkovic et al. 2006

29. Next Steps detailed follow-up of transition disks and other evolved systems – systematic study of accretion via line profiles, veiling – mm measurements of disk masses – high spatial resolution imaging binarity (WFC3, NICMOS) multi-wavelength follow-up of mid-IR variables – optical/NIR photometry – occultation events? – variations of accretion signatures – spectropolarimetry, high resolution polarimetric imaging (NICMOS) – NIR veiling expand age and environment baselines – mass accretion rates of young protostars (COS, NIRSPEC) – disk properties as a function of external UV environment

30. Further in the Future: JWST and beyond Detect optically thin dust around T Tauri stars – early debris disks? Expand environmental samples Simultaneous measures of accretion, disk gas tracers Follow-up of dust structures implied by Spitzer SEDs – high-resolution IR imaging of scattered light from evolved disks to look for further evidence of dust sedimentation – eventually resolve inner holes and the massive planets that may create them? (ALMA, TMT/GMT)