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 ?

NGC 1333: 1 Myr, ~ 102 YSOs

Orion Nebula: 1 Myr, ~ 103 YSOs

NGC 6603: 4 Myr, ~ 104 YSOs

30 Dor: 4 Myr, ~ 105 YSOs

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

OrionAE Aur150 km/s

Infrared view of winter sky (10 - 120 m)

Orion B

Orion A

Orion Nebula

Orion MolecularClouds

13CO 2.6 mm

20 km/s

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

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

850 mdust continuum

Northernpart ofOrion A

SCUBA

Trapezium

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

d253-535 in M43

YSOs with disks and envelopes are common:Facilitate interactions?

M = 20m = 5Mdisk= 1

Close encounters

Moeckel & Bally 05

ProgradeRetrograde

Moeckel & Bally 05Close encounters

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

11.7 m

Gemini STReCS

104 AU

0.5 – 2.2 m

104 AU

11.7 m

104 AU

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

core

annulus

Mass segregation in the Arches

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

The End