1. and the Stellar Upper Mass Limit
Disk fragmentation,
the Brown Dwarf Desert,
and the Stellar Upper Mass Limit
Chris Matzner
University of Toronto
Yuri Levin, U. Leiden Kaitlin Kratter, U. Toronto

2. Disk fragmentation in the main accretion phase
Which protostellar disks accrete stably, and which undergo gravitational fragmentation?
Fragmentation is sensitive to the thermal evolution of the disk…*
*see posters by Kai, Stamatellos
Patel et al 04

3. - Self-luminous disks with negligible irradiation
Gammie
2001
Disk fragments when…
and
Most useful for:
- Self-luminous disks with negligible irradiation
- Setting lower limits on the radius of fragmentation and Mfrag
Rafikov; Whitworth & Stamatellos

4. This form is most useful for:
Gammie
2001
Disk fragments when…
This form is most useful for:
- Disks heated by irradiation as well as viscosity
- Disks with imposed mass accretion

5. A disk fragments if it is cooler than its core
Fed by collapsing mol. core
Implication:
A disk fragments if it is cooler than its core

6. Low-mass star formation
CDM & Y.Levin 2005
Disk fragments when
Accretion heating alone stabilizes the disk for periods less than a few centuries.
see poster by Stamatellos
Outflow cavity
Infall
Innermost
streamline
Reprocessed
starlight
Irradiation by reprocessed starlight can stabilize it out to thousands of years!
see poster by Kai

7. Stabilized by irradiation
Grether & Lineweaver 2006
Stabilized by irradiation
Stabilized by viscous heating

8. Massive star formation
Kratter & CDM 2006
Destabilizing effect
More rapid accretion: fragment when
Stabilizing effect
More luminous central star
Which wins?

9. Kratter & CDM 2006

10. Observer’s-eye view
Kratter & CDM 2006
toroids
disks

11. Fragmentation accelerates as mass increases
Theorists-eye view
Kratter & CDM 2006
McKee & Tan 2003 (fiducial model)
Sharp drop in dust
opacity at high accn
rates
Fragmentation accelerates
as mass increases

12. Stellar upper mass limit
If not radiation pressure, then disk fragmentation?
Few other mechanisms get worse above a threshold

13. Conclusions & Challenges
For Numericists:
Isothermal codes should make too many BDs by disk fragmentation
Radiation-diffusion: stabilize out to century periods
Irradiation, outflow cavity: stabilize even further
For Observers:
Find (or more) companions 150 AU (or less) from young
O stars
Find gravitational spirals in the gas
For Theorists
Brown Dwarf Desert and upper mass limit are both made in disks?
Must account for magnetic fields!
Must model global modes for massive disks.
(w/ M. Krumholz & K. Kratter)