Star and Planet Formation

1
Star and Planet Formation
Sommer term 2007 Henrik Beuther
Sebastian Wolf
16.4 Introduction (H.B. S.W.) 23.4 Physical
processes, heating and cooling, radiation
transfer (H.B.) 30.4 Gravitational collapse
early protostellar evolution I (H.B.) 07.5
Gravitational collapse early protostellar
evolution II (H.B.) 14.5 Protostellar and
pre-main sequence evolution (H.B.) 21.5 Outflows
and jets (H.B.) 28.5 Pfingsten (no lecture) 04.6
Clusters, the initial mass function (IMF),
massive star formation (H.B.) 11.6 Protoplanetary
disks Observations models I (S.W.) 18.6 Gas in
disks, molecules, chemistry, keplerian motions
(H.B.) 25.6 Protoplanetary disks Observations
models II (S.W.) 02.7 Accretion, transport
processes, local structure and stability
(S.W.) 09.7 Planet formation scenarios
(S.W.) 16.7 Extrasolar planets Searching for
other worlds (S.W.) 23.7 Summary and open
questions (H.B. S.W.)
More Information and the current lecture files
http//www.mpia.de/homes/beuther/lecture_ss07.html

and http//www.mpia.de/homes
/swolf/vorlesung/sommer2007.html
Emails beuther_at_mpia.de, swolf_at_mpia.de
2
Summary last week

• The first core contracts until temperatures
  are able to dissociate H2 to H.
• H-region spreads outward, T and P not high
  enough to maintain equilibrium,
• further collapse until H gets collisionally
  ionized. The dynamically stable
• protostar has formed.
• - Accretion luminosity. Definition of low-mass
  protostar can be mass-gaining
• object where the luminosity is dominated by
  accretion.
• - Structure of the protostellar envelope and
  effects of rotation.
• - Stellar structure equations follow numerically
  the protostellar and then
• later the pre-main sequence evolution.
• Convection and deuterium burning.
• End of protostellar/beginning or pre-main
  sequence evolution --gt birthline.
• Pre-main sequence evolution in the
  Hertzsprung-Russel (HR) diagram.
• Connection of HR diagram with protostellar and
  pre-main sequence
• class scheme.

3
Star Formation Paradigm
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Discovery of outflows I
Initially thought to be embedded protostars but
soon spectra were recognized as caused by shock
waves --gt jets and outflows
5
Discovery of outflows II

• In the mid to late 70th, first CO non-Gaussian
  line wing emission detected
• (Kwan Scovile 1976).
• - Bipolar structures, extremely energetic, often
  associated with HH objects

6
HH30, a disk-outflow system
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Outflow multiplicities in Orion
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The prototypical molecular outflow HH211
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Jet entrainment in HH211

• Warmer gas closer to source
• Jet like SiO emission has always
• larger velocities than CO at the
• same projected distance from
• the driving protostar

From Hirano et al. 2006, Palau et al. 2006,
Chandler Richer 2001, Gueth et al. 1999, Shang
et al. 2006
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IRAS 201264104
Lebron et al. 2006
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Mass vs.velocity, energy vs. velocity

• Mass-velocity relation exhibits broken
  power-law, steeper further out
• Energy at high velocities of the same magnitude
  than at low velocities

Lebron et al. 2006
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Outflow/jet precession
13
Jet rotation in DG Tau
Testi et al. 2002
Corotation of disk and jet
Bacciotti et al. 2002
14
General outflow properties

• Jet velocities 100-500 km/s ltgt Outflow
  velocities 10-50 km/s
• Estimated dynamical ages between 103 and 105
  years
• Size between 0.1 and 1 pc
• Force provided by stellar radiation too low
  (middle panel)
• --gt non-radiative processes necessary!

Mass vs. L
Force vs. L
Outflow rate vs. L
Wu et al. 2004, 2005
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Collimation degrees
Collimation degrees (length/width) vary between 1
and 10
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Collimation and pv-structure
HH212 consistent with jet-driving
VLA0548 consistent with wind-driving

• pv-structure of jet- and wind-driven models very
  different
• Often Hubble-law observed --gt increasing
  velocity with increasing distance
• 
  from the protostar

Lee et al. 2001
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Outflow entrainment models I
Basically 4 outflow entrainment models are
discussed in the literature Turbulent jet
entrainment model - Working surfaces at the
jet boundary layer caused by Kelvin-Helmholtz
instabilities form viscous mixing layer
entraining molecular gas. --gt The mixing
layer grows with time and whole outflow gets
turbulent. - Broken power-law of
mass-velocity relation is reproduced, but
velocity decreases with distance from
source --gt opposite to observations Jet-bow
shock model - As jet impact on ambient gas,
bow shocks are formed at head of jet. High
pressure gas is ejected sideways, creating a
broader bow shock entraining the ambient
gas. Episodic ejection produces chains of knots
and shocks. - Numerical modeling reproduce
many observables, e.g. Hubble-law.
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Jet simulations I
3-dimensional hydrodynamic simulations, including
H, C and O chemistry and cooling of the gas, this
is a pulsed jet.
Rosen Smith 2004
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Jet simulations II small precession
Rosen Smith 2004
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Jet simulations III, large precession
Rosen Smith 2004
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Outflow entrainment models II
Wide-angle wind model - A wide-angle wind
blows into ambient gas forming a thin swept-up
shell. Different degrees of collimation
can be explained by different density
structures of the ambient gas. - Attractive
models for older and low collimated
outflows. Circulation model -
Molecular gas is not entrained by underlying jet
or wind, but it is rather infalling gas
that was deflected from the central protostar in
a region of high MHD pressure. - This
model was proposed to explain also massive
outflows because it was originally
considered difficult to entrain that large
amounts of gas. Maybe not necessary today
anymore
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Outflow entrainment models III
Arce et al. 2002
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Jet launching

• Large consensus that outflows are likely driven
  by magneto-
• centrifugal winds from open magnetic field
  lines anchored on
• rotating circumstellar accretion disks.
• Two main competing theories disk winds ltgt
  X-winds
• Are they launched from a very small area of the
  disk close to the
• truncation radius (X-wind), or over larger
  areas of the disk (disk wind)?

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Jet-launching Disk winds I
Banerjee Pudritz 2006

• Infalling core pinches magnetic field.
• If poloidal magnetic field component
• has angle larger 30 from vertical,
• centrifugal forces can launch matter-
• loaded wind along field lines from disk
• surface.
• Wind transports away from 60 to 100
• of disk angular momentum.

Recent review Pudritz et al. 2006
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Jet-launching Disk winds II
t1.3x105 yr
t9.66x105 yr
Toroidal magnetic field

• On larger scales, a strong toroidal
• magnetic field builds up during collapse.
• At large radii (outside Alfven radius rA, the
• radius where kin. energy equals magn.
• energy) Bf/Bp much larger than 1
• --gt collimation via Lorentz-force FLjzBf

Banerjee Pudritz 2006
26
X-winds

• The wind is launched magneto-centrifugally from
  the inner
• co-rotation radius of the accretion disk
  (0.03AU)

27
Jet-launching points and angular momenta

• From toroidal and poloidal velocities, one
• infers footpoints r0, where gas comes from
• --gt outer r0 for the blue and red wing are
• about 0.4 and 1.6 AU (lower limits)
• --gt consistent with disk winds
• About 2/3 of the disk angular momentum
• may be carried away by jet.

Woitas et al. 2005
28
Impact on surrounding cloud

• Entrain large amounts of cloud mass with high
  energies.
• Potentially partly responsible to maintain
  turbulence in cloud.
• Can finally disrupt the cores to stop any
  further accretion.
• Can erode the clouds and alter their velocity
  structure.
• May trigger collapse in neighboring cores.
• Via shock interactions heat the cloud.
• Alter the chemical properties.

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Outflow chemistry
Bachiller et al. 2001
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Summary

• Outflows and jets are ubiquitous and necessary
  phenomena
• in star formation.
• Transport angular momentum away from protostar.
• The are likely formed by magneto-centrifugal
  disk-winds.
• Collimation is caused by Lorentz forces.
• Gas entrainment can be due to various processes
  turbulent
• entrainment, bow-shocks, wide-angle winds,
  circulation
• They inject significant amounts of energy in the
  ISM, may be
• important to maintain turbulence.
• Disrupt at some stage their maternal clouds.
• Often point back to the forming star

31
Star and Planet Formation
Sommer term 2007 Henrik Beuther
Sebastian Wolf
16.4 Introduction (H.B. S.W.) 23.4 Physical
processes, heating and cooling, radiation
transfer (H.B.) 30.4 Gravitational collapse
early protostellar evolution I (H.B.) 07.5
Gravitational collapse early protostellar
evolution II (H.B.) 14.5 Protostellar and
pre-main sequence evolution (H.B.) 21.5 Outflows
and jets (H.B.) 28.5 Pfingsten (no lecture) 04.6
Clusters, the initial mass function (IMF),
massive star formation (H.B.) 11.6 Protoplanetary
disks Observations models I (S.W.) 18.6 Gas in
disks, molecules, chemistry, keplerian motions
(H.B.) 25.6 Protoplanetary disks Observations
models II (S.W.) 02.7 Accretion, transport
processes, local structure and stability
(S.W.) 09.7 Planet formation scenarios
(S.W.) 16.7 Extrasolar planets Searching for
other worlds (S.W.) 23.7 Summary and open
questions (H.B. S.W.)
More Information and the current lecture files
http//www.mpia.de/homes/beuther/lecture_ss07.html

and http//www.mpia.de/homes
/swolf/vorlesung/sommer2007.html
Emails beuther_at_mpia.de, swolf_at_mpia.de