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Disk structure_ reprocessing stellar radiation

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					 Chapter 6: Planetological
foundations for origins of life
     A. Major questions in star formation:

1. What determines the stellar mass spectrum
   (the “initial mass spectrum” IMF)?
2. How do individual stars/disks/jets form?
3. Do all stars form in the same way? (both low
   and high mass stars)?
4. How does star formation affect planet
   formation? [what accounts for weird
   extrasolar planetary systems?]
Star formation in the Milky Way:
Stars form in massive clouds of dusty,
cold, molecular gas
- To detect gas - map millimetre wave
emission from carbon monoxide
molecule.
- To detect dust - map sub-millimetre
emission from dust grains (eg. Use
James Clerk Maxwell Telescope – on
top of Mauna Kea volcano - Hawaii)
Radio
Star formation in the Galaxy

                      The Galactic Center
                      in visible Light




Optical
     Optical images and infrared
     images of the Orion Nebula




IRAS satellite: sensitive at wavelengths 10 – 100 microns
                     Orion GMC - and the Orion Nebula Cluster
                     Most stars form as members of star clusters
                     and not in isolation:
                         Major clue to origin of IMF…..




Johnstone et al (2000)
Super-massive star clusters




       Star cluster in the Large Magellanic Cloud, (HST image)
The Origin of Stellar
Masses:
Formation of Molecular
Cloud Cores?

 • Numerous small
 dense gas “cores”
 within a clump.
 Individual stars form in
 cores – typically 0.04
 pc in size




  (Motte et al 2001)
Origin of stellar masses – have same distribution in mass as
small gas cores
      How do nearby stars form in
      molecular clouds?
   Clouds are turbulent
   Turbulence produces density fluctuations that
    resemble rotating cores.
   Simulations and theory show that “turbulent
    fragmentation” can produce core mass
    spectrum.
   Turbulence is universal – may imply
    universality of the IMF
Largest star
formation
simulation ever
done:
100,000 cpu hours!
- Begin with: cloud
is 1.2 light-years
across, contains
50 solar masses of
gas.
- Initial turbulence
in the cloud
fragments it – then
gravity pulls
regions together to
form “cores”
Turbulence and star
cluster simulation

 - shows highly
 filamented structure
 - shows many small
 overdense regions
 which can be
 identified with
 “cores”.
 - cores formed
 through turbulent
 fragmentation
                        Tilley & Pudritz (2004)
   Massive star
    formation –
    filamentary
    accretion
    FLASH – Adaptive
    Mesh Refinement
    (AMR) simulation:
    (Banerjee, Pudritz, &
    Anderson 2006: start
    with TP04 )
   Collapse along
    filament into a
    forming disk...
Tilley & Pudritz ‘04 – hydro simulations of turbulent fragmentation




                M peak  103 M J  103 M tot / nJ
Simulating star
  formation in
  magnetized
  clouds (Tilley
  & Pudritz
  2005)

Turbulence
  breaks up
  clouds into
  dense cores
  in which
  stars form
        Gravitational collapse of core:
        formation of a star/disk/jet




Infrared image Barnard 68 (Alves et al 2001): excellent fit with
Bonner-Ebert model (pressure truncated isothermal sphere)
      Disks around young – and
      old stars




Orion Proplyd – star in formation   Submm image of Epsilon Eridanni
                                    Greaves et al (1998)
Disks in the Orion nebula…
               Disk structure: reprocessing stellar radiation
                                  Submm     Infrared       Optical
     Radiative resprocessing:
   hydrostatic equilibrium disk
             models
1: Disk Surface Tds
2: Disk Interior Ti




                                     Chiang and Goldreich (1997)
  Chemisty in protoplanetary disks: mm wavelengths




(Aikawa et al 2002): distribution of T (top row) and n (bottom row),
    in D’Allessio et al model. Columns correspond to 3 different
    accretion rates. Top: dark is low CO/H2, grey is higher:
Molecular Probes of Inner Disks

                        H2 UV, NIR, MIR
           H2O ro-vib
          OH v=1

               CO v=1
     CO v=2


         0.1 AU                1 AU       10 AU
        ~1000 K               ~200 K      ~50 K
         Are the organic precursor molecules for life
              common in planet-forming disks?

•   The MIR is rich in transitions of organic molecules




        Hydrocarbons in massive protostar NGC 7538
Collapse & disk formation: Density
      (Banerjee & Pudritz, 2004)
Jets are strongly correlated with disk properties… what
produces jets? Magnetic fields are crucial…
Collapse of a magnetized core: produce outflows by “magnetic
            centrifuge”. (Banerjee & Pudritz 2006)
Jets as disk winds: (Banerjee & Pudritz 2006)
 - launch inside 0.07 AU
   (separated by 5 month interval)
- jets rotate and carry off angular momentum of disk
- spin of protostellar core at this early time?
Universality – do all stars form in the same way?


Brown dwarfs: observed to have disks and jets!
        (eg. Whelan et al 2006 for 60 MJupiter BD).

Massive YSO jets: massive accretion > 0.001 solar
  masses/yr prevent radiation pressure from blowing
  away the infall:
   -> massive star formation by accretion picture too?
       (McKee & Tan 2003)
  - some massive stars observed to have both disks
  and jets.

				
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posted:12/5/2012
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