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@mpia.de, swolf@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 --> 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

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

5. Snell et al. 1980 Bachiller et al. 1990 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

7. Stanke et al. 2002 Outflow multiplicities in Orion

8. The prototypical molecular outflow HH211

9. 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

10. IRAS 20126+4104 Lebron et al. 2006

11. 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

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

13. red blue 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 <==> 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) • --> non-radiative processes necessary! Mass vs. L Force vs. L Outflow rate vs. L Wu et al. 2004, 2005

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

16. 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

17. Gueth et al. 1999 Raga et al. 1993 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. --> 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.

18. 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

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

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

21. Fiege & Henriksen 1996 Shu et al. 1991 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 …

22. Outflow entrainment models III Arce et al. 2002

23. 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)?

24. Jet-launching: Disk winds I 5 months later Collapse: 6.81 x 104 yr 1AU~ 1.5x1013cm 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

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

26. Shu et al. 2000 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 Spectro-Astrometry r0,in corresponds approximately to corotation radius ~ 0.03 AU • From toroidal and poloidal velocities, one • infers 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

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.

29. Outflow chemistry Bachiller et al. 2001

30. 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@mpia.de, swolf@mpia.de