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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. Disk fragmentation in the main accretion phase.

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Presentation Transcript
slide1

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

slide2

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

slide3

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

slide4

Gammie

2001

Disk fragments when…

This form is most useful for:

- Disks heated by irradiation as well as viscosity

- Disks with imposed mass accretion

slide5

Fed by collapsing mol. core

Implication:

A disk fragments if it is cooler than its core

slide6

Innermost

streamline

Outflow cavity

Reprocessed

starlight

Infall

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

Irradiation by reprocessed starlight can stabilize it out to thousands of years!

see poster by Kai

slide7

Grether & Lineweaver 2006

Stabilized by irradiation

Stabilized by viscous heating

slide8

Massive star formation

Kratter & CDM 2006

Destabilizing effect

More rapid accretion: fragment when

Stabilizing effect

More luminous central star

Which wins?

slide10

Observer’s-eye view

Kratter & CDM 2006

toroids

disks

slide11

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

slide12

Stellar upper mass limit

If not radiation pressure, then disk fragmentation?

Few other mechanisms get worse above a threshold

slide13

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 0.1-1 (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)