1. Kaitlin Kratter Harvard CfA / U Toronto Chris Matzner (U Toronto), Mark Krumholz (UCSC), Richard Klein (LLNL/Berkeley) Townsville, Sep 17th, 2010 Binary Formation via Disk Fragmentation Massive Star Formation

2. 1. Make Disk 2. Dump mass on at high rates 3. Drive up mass, density so that 4. Toomre (1964) instability produces small fragment 5. Fragment accretes from the disk and infalling material Mechanism for Binary Formation via Disk Fragmentation Kratter et al, 2008, 2010a,b

3. Simple example of accretion driven fragmentation and subsequent growth box tracks “lagrangian” radius Kratter et al, 2010a

4. Disk-born binaries NOT a new idea (e.g. Adams et al 1989, Bonnell & Bate 1994). Why reconsider? Previously discounted because: observed disks are low in mass ( T Tauri disks) (e.g. Eisner & Carpenter 2006, Andrews & Williams 2009) fragments are small = mass ratios must all be small Only recently (re)considered for massive stars because disk observations are new / ongoing Motivation? Why Now?

5. Why different for massive stars? 1. >75% of O stars (and many B) are in Binaries / Multiples (Mason et al 2009) 2. Propensity for disk fragmentation increases with primary mass, i.e. high accretion rates Kratter & Matzner, 2006

6. due to intense radiation from very massive stars and a drop in dust opacity at ~1050K, disks around stars above ~120 solar masses have truncated disks Disks and the Stellar upper mass limits Kratter & Matzner, 2006

7. Implications for Multiplicity What is correspondence with real systems? Final outcome will depend on evolution of infalling angular momentum mass ratio: function of lag between formation and angular momentum scaling Observations of orientation? Turner et al 2008

8. Evidence for a disk origin? Hale 1994 Do torques from outer disk drive to smaller radii? What about hierarchical multiples? Population unconstrained... multiples?

9. Disks and Binaries: Massive Twins? Mass ratio vs separation is somewhat consistent mass transfer may also explain mass ratio (Krumholz and Thompson, 2007) Kratter, Matzner, & Krumholz, 2008 Time vs Mass Ratio

10. Binary Behavior Equalize in mass Movement relative to outer disk radius depends on torque balance Time vs Mass Ratio Time vs Separation