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John Bally
Center for Astrophysics and Space Astronomy
Department of Astrophysical and Planetary Sciences University of Colorado, Boulder
Star FormationStar Formation inin ClustersClusters
OutlineOutline• Most stars form in clusters: - Transient clusters => T, OB associations > 90% of stars: < few x cross ~ r / - Open clusters: few % of stars: ~ 10 - 103 x cross - Globular clusters: <<1% of stars: >> 103 x cross • Dissipation by cores, envelopes, disks: - Collapse, interactions, IMF, mergers (?)• Formation of clusters: Feedback from massive stars GMC: Vescape < CII ~ 10 km/s => Transient?
Vescape > CII ~ 10 km/s => Open ?
Vescape >> CII ~ 10 km/s => SSC => Globular ?
Cluster Formation ICluster Formation I
• Turbulent Giant Molecular Clouds: - Dissipation - Shocks => transient clumps - Occasionally, clumps bound by gravity - Graviational collapse: r ~ 107, ~ 1021
- 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
Cluster Formation IICluster 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?
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
Orion belowthe Belt:
Horsehead Nebula
Orion Nebula
NGC 2024 (OB1 d)
Orionis (c)
NGC 1977
OriNGC1980: Source of Col + AE Aur ; V ~ 150 km/s runaways, 2.6 Myr ago
NGC 1981
Ori OB1c
Ori OB1d
NKLTrapezium
OMC1-S
(L = 105 Lo
t << 105 yr)
(L = 104 Lo ,
t < 105 yr)
(L = 105 Lo
t < 105 yr )
OMC 1 Outflow
t = 3,000 yr)
Orion NebulaOrion Nebula
Trapezium clusterTrapezium cluster
Proper motions:Van Altena et al. 88
Vesc ~ 6 km s-1
2.6
1.8
5 2.5
OrionBN/KLH2
OMC1-S Jets
CO
HH
NICFPSAPO 3.5 mFirst light21 Nov 04
HH 202
Zapata jet +HH 625
HH 269
HH 530Schmid-Burgk jet
HH 529
HH 203/204 HH 528
High-velocity stars: source I, BN (Rodriguez et al. 2005)
BN: ~ 30 km s-1
I: ~ 13 km s-1
i ~ 24o
t ~ 500 yrs
Arches ClusterGalactic Center
• Age ~ 2 Myr
• ~ 50 OB stars
• 103-4 stars (?)
• 3 X 105 stars pc-3
Stolte et al. (2005)ApJ, 628, L113
Shallow, broken IMF (Arches) Stolte et al. (2005)• Mass segregation• Low M cut-off, bias towards massive stars• Dynamical evolution?
Background
Salpeter = -1.35
Massive Stars: HII, SNe & SFEMassive Stars: HII, SNe & SFE• Ionization (HII): - Photo-ionization => Cs ~ 10 km/s - Cs > Vescape => Fast blow-out of gas => OB star stops star formation - If SFE < 0.3, blow-out < tcross => Unbound association - Cs < Vescape => Slow removal of gas
=> Open cluster• Supernovae (SN) - MGMC Vesc < Meject Veject => SN stops star formation=> Open cluster - MGMC Vesc > Meject Veject (supermassive core) => Globular cluster
ConclusionsConclusions• 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: - Vescape < CII ~ 10 km/s => Transient association
- Vescape > CII ~ 10 km/s => Open Cluster
- Vescape >> CII ~ 10 km/s => SSC => Globular Cluster