1. The University of Western Ontario Shantanu Basu and Eduard Vorobyov Cores to Disks to Protostars: The Effect of the Core Envelope on Accretion and Disk Evolution KIK Meeting, Stars to Halos: The Scale Challenge, July 19, 2006

2. Stages of Star Formation: The Scale Challenge Core collapse scale to disk accretion/outflow scale – over a factor 1000. ~ 20,000 AUseveral AU

3. An Evolutionary Sequence for YSO’s Based on spectral energy distributions (SED’s) Whitney et al. (2003) SED for different inclination angles i Circumstellar matter distribution

4. Outflow power Envelope mass filled circlesopen circles Class 0 vs. Class I. Differences in Dynamics? Bontemps et al. (1996), Henriksen, André, & Bontemps (1997). Class 0’s drive much more powerful outflows.

5. A dynamical explanation of Class 0/I phases Henriksen, André, & Bontemps (1997) Flat inner region power law profile, r -2 steep drop-off due to finite mass reservoir radius density time Initial large and declining rate intermediate self-similar rate terminal decline due to finite mass reservoir t < 0, before protostar forms t > 0, after protostar forms pressure-free collapse model

6. A dynamical explanation of Class 0/I phases Henriksen, André, & Bontemps (1997) t > 0 evolution CLASS 0 – open circles CLASS I – filled circles Many (most?) of the Class I objects are in the TERMINAL accretion phase!! Outflow power Envelope mass

7. sound speed c s =0.2 km/s Spherical hydrodynamic collapse model Vorobyov & Basu (2005) – focus on effect of finite mass reservoir t < 0, i.e., before central protostar is formed Start with modified isothermal sphere profile; similar to B-E sphere Temporal sequence 1,2,…5.

8. Spherical hydrodynamic collapse model Vorobyov & Basu (2005) t > 0, mass accretion rate onto central protostar (actually disk). low mass core intermediate mass core 5 M sun 24 M sun Numbers in parentheses = % of mass remaining in envelope at times of protostar formation – a sink cell is introduced early terminal self-similar

9. Spherical hydrodynamic collapse model low mass core intermediate mass core Vorobyov & Basu (2005) Proposed accretion phases: Class 0: all accretion PRIOR to terminal phase. Class I: all accretion AFTER terminal phase begins. The LUMINOSITY PEAK separates the two classes. Many (most?) cores will NOT experience the fully self-similar collapse phase. F CO = outflow power, proportional to,bolometric luminosity 5 M sun 24 M sun

10. Protostar (sink cell) ~ 10 AU ~ 1-2 M  ~ 100 AU Magnetohydrodynamic equations (r,  ) in the thin-disk approximation. Flattened molecular cloud core ~ 0.1 pc ~20,000 AU Infalling envelope disk Numerical simulations of cloud core collapse  Logarithmically spaced grid in the r-direction. 128 x 128 or 256 x 256. Fast convolution method to find the gravitational potential . No restrictive periodic boundaries;  Self-consistent treatment of the disk-envelope interaction;  Long integration times (~ Myr).

11. Collapse of a disklike cloud Vorobyov & Basu (2006) No rotation in this model Numbers in parentheses = % of mass remaining in envelope protostar forms here

12. Mass accretion bursts and the Q-parameter Black line - mass accretion rate onto the protostar. Red line – the Q-parameter The disk is strongly gravitationally unstable when the bursts occur Smooth mode Burst mode Rotation now included disk forms here

13. Self-consistent formation and evolution of the protostellar disk Mass infall rate onto the protostar Evolution of the protostellar disk

14. Spiral structure and protoplanetary embryo formation Quiescent phase, between burstsJust prior to a burst

15. Mass accretion bursts and the Q-parameter Black line - mass accretion rate onto the protostar; Red line – the Q-parameter The disk is strongly gravitationally unstable when the bursts occur Smooth mode Burst mode

16. FU Ori-like luminosity outbursts and the gravitational torque Black line – the accretion luminosity Red line – the integrated gravitational torque Spiral gravitational field is responsible for the outbursts

17. Dense clumps and gravitational torques Spatial distribution of negative gravitational torque, in grayscale. Azimuthally averaged surface density (solid line) and gravitational torque (dashed line).

18. Hartmann (1998) – empirical inference, based on ideas advocated by Kenyon et al. (1990). Accretion history of young protostars Vorobyov & Basu (2006) – theoretical calculation of disk formation and evolution

19. Protostellar disks can be gravitationally unstable on large scales Theoretical models (e.g. Larson 1984) Numerous numerical simulations (Bodenheimer, Boss, Laughlin, Bate, Wadsley, Rice, Lodato, Durisen, Vorobyov & Basu, and many others) Observations of non-axisymmetric structures in protostellar disks of AB Aurigae (Fukagawa et al. 2004) and HD 100546 (Grady et al. 2001) HD 100546

20. Conclusions Accretion phase (t > 0) consists of - early rapid and declining accretion (L bol is increasing) - intermediate (self-similar) accretion (L bol is increasing) - terminal declining accretion (L bol is decreasing) Many (most?) class I objects already in the terminal phase (Henriksen et al. 1997) Start of terminal accretion phase coincides with luminosity peak. We suggest this as a physical dividing line between class 0 and class I objects. From spherical or nonrotating disklike models

21. Conclusions Protostellar disks are gravitationally unstable and can form protoplanetary embryos via direct gravitational instability. Accretion from the envelope drives disk evolution and instability. However, most embryos will be driven onto the protostar due to the efficient exchange of angular momentum between embryos and the spiral arms! Only those embryos that form in the outer parts of spiral arms, or perhaps at very late times, may ultimately survive. The episodes of embryo infall provide an explanation for the FU Ori eruptions. The authors are thankful to Takahiro Kudoh and Sergey Khan for the help with preparing the animation of protostellar disks From rotating disklike models