1. Sternentstehung - Star Formation
Sommersemester 2006
Henrik Beuther & Thomas Henning
24.4 Today: Introduction & Overview
Public Holiday: Tag der Arbeit
15.5 Physical processes, heating & cooling, cloud thermal structure
22.5 Physical processes, heating & cooling, cloud thermal structure (H. Linz)
29.5 Basic gravitational collapse models I
Public Holiday: Pfingstmontag
12.6 Basic gravitational collapse models II
19.6 Accretion disks
26.6 Molecular outflow and jets
Protostellar evolution, the stellar birthline
10.7 Cluster formation and the Initial Mass Function
Massive star formation, summary and outlook
Extragalactic star formation
More Information and the current lecture files:

2. Summary last week: Accretion disks
Bergin et al. 2006
Chang & Goldreich 1997
Guilloteau et al. 1998
DM Tau
CO(2-1)
Hartmann 2000
Strassmeier et al.
2005

3. Ambipolar diffusion update
Rao et al. 2006

4. Star Formation Paradigm

5. Discovery of outflows I
Herbig 1950, 1951; Haro 1952, 1953
Initially thought to be embedded protostars but soon spectra were
recognized as caused by shock waves --> jets and outflows

6. Discovery of outflows II
Bachiller et al. 1990
Snell et al. 1980
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

7. HH30, a disk-outflow system

8. Outflow multiplicities in Orion
Stanke et al. 2002

9. The prototypical molecular outflow HH211

10. 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

11. IRAS
Lebron et al. 2006

12. 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

13. Outflow/jet precession
Stanke 2003
Fendt & Zinnecker 1998

14. Jet rotation in DG Tau Corotation of disk and jet red blue
Testi et al. 2002
Corotation of disk and jet
Bacciotti et al. 2002

15. General outflow properties
Jet velocities km/s <==> Outflow velocities 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)
--> non-radiative processes necessary!
Mass vs. L Force vs. L Outflow rate vs. L
Wu et al. 2004, 2005

16. Jet sizes
Stanke 2003

17. Collimation degrees
HH211, Gueth et al. 1999
Collimation degrees (length/width) vary between 1 and 10
Wu et al. 2004

18. 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 --> increasing velocity with increasing distance
from the protostar
Lee et al. 2001

19. Outflow entrainment models I
Gueth et al. 1999
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.
--> 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 --> 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.
Raga et al. 1993

20. 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

21. Jet simulations II: small precession
Rosen &
Smith 2004

22. Jet simulations III, large precession
Rosen &
Smith 2004

23. Outflow entrainment models II
Fiege & Henriksen 1996

Wide-angle wind model
- A wide-angle wind blows into ambient gas forming a this 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 models were proposed to explain also massive outflows because
it was originally considered difficult to entrain that large amounts of gas.
Maybe not necessary today anymore …
Shu et al. 1991

24. Outflow entrainment models III
Arce et al. 2002

25. 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 <==> 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)?

26. Jet-launching: Disk winds I
Collapse: 6.81 x 104 yr
5 months later
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.
1AU~
1.5x1013cm
Recent review: Pudritz et al. 2006

27. Jet-launching: Disk winds II
t=1.3x105 yr t=9.66x105 yr
1AU~
1.5x1013cm
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
--> collimation via Lorentz-force FL~jzBf
Banerjee & Pudritz 2006

28. X-winds The wind is launched magneto-centrifugally from the inner
Shu et al. 2000
The wind is launched magneto-centrifugally from the inner
co-rotation radius of the accretion disk (~0.03AU)

29. Jet-launching points and angular momenta
Spectro-Astrometry
r0,in corresponds
approximately to
corotation radius
~ 0.03 AU
From toroidal and poloidal velocities, one
infer footpoints r0, where gas comes from
--> outer r0 for the blue and red wing are
about 0.4 and 1.6 AU (lower limits)
--> consistent with disk winds
About 2/3 of the disk angular momentum
may be carried away by jet.
Woitas et al. 2005

30. 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.

31. Outflow chemistry
Bachiller et al. 2001

32. Outflows and Jets: Theory and Observations
Summary
Outflows and jets are ubiquitous and necessary phenomena
in star formation.
Transport angular momentum away from protostar.
The are likely formed by magneto-centrigugal 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
Next semester:
Outflows and Jets: Theory and Observations
H. Beuther & C. Fendt

33. Sternentstehung - Star Formation
Sommersemester 2006
Henrik Beuther & Thomas Henning
24.4 Today: Introduction & Overview
Public Holiday: Tag der Arbeit
15.5 Physical processes, heating & cooling, cloud thermal structure
22.5 Physical processes, heating & cooling, cloud thermal structure (H. Linz)
29.5 Basic gravitational collapse models I
Public Holiday: Pfingstmontag
12.6 Basic gravitational collapse models II
19.6 Accretion disks
26.6 Molecular outflow and jets
Protostellar evolution, the stellar birthline
10.7 Cluster formation and the Initial Mass Function
Massive star formation, summary and outlook
Extragalactic star formation
More Information and the current lecture files: