1. John Bally Center for Astrophysics and Space Astronomy Department of Astrophysical and Planetary Sciences University of Colorado, Boulder Star Formation Star Formation in in Clusters Clusters

2. Outline Outline Most stars form in clusters: - Transient clusters => T, OB associations > 90% of stars:  < few x  cross ~ r /  - Open clusters: few % of stars:  ~ 10 - 10 3 x  cross - Globular clusters: > 10 3 x  cross Dissipation by cores, envelopes, disks: - Collapse, interactions, IMF, mergers (?) Formation of clusters: Feedback from massive stars GMC: V escape Transient? V escape > C II ~ 10 km/s => Open ? V escape >> C II ~ 10 km/s => SSC => Globular ?

3. NGC 1333: 1 Myr, ~ 10 2 YSOs

4. Orion Nebula: 1 Myr, ~ 10 3 YSOs

5. NGC 6603: 4 Myr, ~ 10 4 YSOs

6. 30 Dor: 4 Myr, ~ 10 5 YSOs

7. Cluster Formation I Cluster Formation I Turbulent Giant Molecular Clouds: - Dissipation - Shocks => transient clumps - Occasionally, clumps bound by gravity - Graviational collapse:  r ~ 10 7,  ~ 10 21 - Fragmentation => Cluster Star formation: - Competitive accretion: - dM/dt  M, dM/dt high in dense core => Range of masses - Feedback: Outflows, UV, supernovae (SNe) - Interactions: => IMF, binaries, mergers

8. Cluster Formation II Cluster Formation II Interactions: - Facilitated by disks, proto-star envelopes - Capture formed binaries Binary  single star Binary  binary - Stellar mergers (?) => high mass stars, GRBs? Ejection of star(s) : Hardening of surviving binary - High-velocity runaway stars (V > 50 km s -1 ) - Intermediate-velocity runaways (10 <V < 50 km s -1 ) - Field multiple star distribution? Mass-segregation Initial Mass Function - Ejection => stop accretion => final stellar mass - Determined by interactions in N-body system?

9. The Orion/Eridanus Bubble (H  ): d=180 to 500pc; l > 300 pc Orion OB1 Association: ~40 > 8 M stars: ~20 SN in 10 Myr 1a (8 - 12 Myr; d ~ 350 pc)) 1b (3 -6 Myr; d ~ 420 pc) 1c (2 - 6 Myr; d ~ 420 pc) 1d (<2 Myr; d ~ 460 pc) Ori (< 3 Myr) Barnards's Loop Eridanus Loop

10. Orion AE Aur 150 km/s

11. Infrared view of winter sky (10 - 120  m)

12. Orion B Orion A Orion Nebula Orion Molecular Clouds 13 CO 2.6 mm

14. 20 km/s

15. Orion below the Belt: Horsehead Nebula Orion Nebula NGC 2024 (OB1 d)  Orionis (  c) NGC 1977  Ori NGC1980: Source of  Col + AE Aur ; V ~ 150 km/s runaways, 2.6 Myr ago NGC 1981 Ori OB1c Ori OB1d

16. CO (Bally et al.) 2MASS stars (Carpenter et al.)

17. 850  m dust continuum Northern part of Orion A SCUBA Trapezium

18.  NKL  Trapezium  OMC1-S (L = 10 5 L o t << 10 5 yr) (L = 10 4 L o, t < 10 5 yr) (L = 10 5 L o t < 10 5 yr ) OMC 1 Outflow   t = 3,000 yr) Orion Nebula

19. Trapezium cluster Proper motions: Van Altena et al. 88 V esc ~ 6 km s -1 2.6 1.8 5 2.5

20. d253-535 in M43 YSOs with disks and envelopes are common: Facilitate interactions?

21. M = 20 m = 5 M disk = 1 Close encounters Moeckel & Bally 05

22. ProgradeRetrograde Moeckel & Bally 05Close encounters

25. Orion BN/KL H 2 OMC1-S Jets CO HH NICFPS APO 3.5 m First light 21 Nov 04 HH 202 Zapata jet + HH 625 HH 269 HH 530 Schmid-Burgk jet HH 529 HH 203/204 HH 528

26. 11.7  m Gemini S TReCS 10 4 AU

27. 0.5 – 2.2  m 10 4 AU

28. 11.7  m 10 4 AU

29. High-velocity stars: source I, BN (Rodriguez et al. 2005) BN: ~ 30 km s -1 I: ~ 13 km s -1 i ~ 24 o t ~ 500 yrs

30. Arches Cluster Galactic Center Age ~ 2 Myr ~ 50 OB stars 10 3-4 stars (?) 3 X 10 5 stars pc -3 Stolte et al. (2005) ApJ, 628, L113

31. Shallow, broken IMF (Arches) Stolte et al. (2005) Mass segregation Low M cut-off, bias towards massive stars Dynamical evolution? Background  Salpeter = -1.35

32. core annulus Mass segregation in the Arches

33. Massive Stars: HII, SNe & SFE Massive Stars: HII, SNe & SFE Ionization (HII): - Photo-ionization => C s ~ 10 km/s - C s > V escape => Fast blow-out of gas => OB star stops star formation - If SFE < 0.3,  blow-out < t cross => Unbound association - C s Slow removal of gas => Open cluster Supernovae (SN) - M GMC V esc < M eject V eject => SN stops star formation=> Open cluster - M GMC V esc > M eject V eject (supermassive core) => Globular cluster

34. Conclusions Conclusions Most stars form in transient clusters: - Transient T / OB associations Circumstellar gas: - Dissipation - Mass segregation - Capture formed binaries - High-velocity stars - Mergers Impact of Massive Star UV, SN: - V escape Transient association - V escape > C II ~ 10 km/s => Open Cluster - V escape >> C II ~ 10 km/s => SSC => Globular Cluster

35. The End