Disk Disruption in YoungEmbedded Clusters

Eva-Marie ProszkowUniversity of Michigan

18 May 2006

Fred Adams (University of Michigan)Phil Myers (Harvard Smithsonian CfA)

Marco Fatuzzo (Xavier University)

Introduction

• Environmental effects on planet formation:

– disruptive FUV radiation– scattering interactions

between star-disk systems• Large (>1000 stars), dense

clusters disrupt disk and planet formation

• Small (<100 stars) clusters don’t

• Intermediate sized clusters (100 < N < 1000 members)

Virial Ratio Q ≡ |K/W|Virial Q = 0.5 SubvirialQ = 0.04

Mass Segregationlargest star at center of cluster

Simulations of Embedded Clusters

Cluster Membership

Cluster Radius

Initial Stellar DensityGas Distribution

Star Formation Efficiency 0.33Embedded Epoch t = 0–5

MyrStar Formation Epoch t = 0-1

Myr

Mass Profiles

SubvirialVirial

Simulation p r0 a100 Subvirial

0.69 0.39 2

100 Virial 0.44 0.70 3300 Subvirial

0.79 0.64 2

300 Virial 0.49 1.19 31000 Subvirial

0.82 1.11 2

1000 Virial 0.59 1.96 3

– Photoevaporation of a circumstellar disk (Shu et al., 1993)

– Radiation from the background cluster often dominates radiation from the parent star (Johnstone et al., 1998; Adams & Myers, 2001)

– FUV radiation (6 eV < h < 13.6 eV) is more important in this process than EUV radiation.

– FUV flux of G0 = 3000 will truncate a circumstellar disk to rd over 10 Myr, where

(Adams et al., 2004)

Effects of Cluster Radiation on Forming Solar Systems

Calculation of the Radiation Field

Fundamental Assumptions– Cluster size N → N primaries (ignore binary companions)– No gas or dust attenuation of FUV radiation– Stellar FUV luminosity is only a function of mass– Adopt Meader’s models for total stellar luminosity and temperature

as a function of mass

Sample IMF LFUV(N)

<LFUV> = 8.20 x 1035 ergs/s

Photoevaporation in the Simulated Clusters

Simulation reff (pc) G0 mean

rmed (pc)

G0 median

100 Subvirial 0.080 66,500 0.323 359100 Virial 0.112 34,300 0.387 250300 Subvirial 0.126 81,000 0.549 1,550300 Virial 0.181 39,000 0.687 9921000 Subvirial

0.197 109,600 0.955 3,600

1000 Virial 0.348 35,200 1.25 2,060Around solar mass stars, FUV radiation will not evaporate

enough of the disk to prevent gas giant formation

Radial Probability Distributions

Closest Approach Distributions

Simulation 0 bC (AU)100 Subvirial 0.166 1.50 713100 Virial 0.059

81.43 1430

300 Subvirial 0.0957

1.71 1030

300 Virial 0.0256

1.63 2310

1000 Subvirial

0.0724

1.88 1190

1000 Virial 0.0101

1.77 3650A typical star will experience one encounter with the characteristic impact parameter bC during a 10 Myr time span.

Solar System Scattering in Clusters

~100,000 7-body scattering experiments to determine cross sections for solar system disruption

2.0 M 1.0 M

0.5 M 0.25 M

Solar System Scattering in Clusters

Ejection Rate per Star (for a given mass)

Integrate over IMF(normalized to cluster

size)

Subvirial N=300 Cluster0 = 0.096 = 1.7

J = 0.15 per Myr

1-2 Jupiters are ejected in 10 Myr

Less than number of ejections from internal solar system

scattering (Moorhead & Adams 2005)

Interaction Rate per Star

Disk Truncation due to Close Encounters

Circumstellar disks are truncated by close encounters to radii ~1/3 the distance of closest

approach(Kobayashi & Ida 2001)

Simulation bC (AU) rd (AU)100 Subvirial 713 237100 Virial 1430 476300 Subvirial 1030 343300 Virial 2310 7701000 Subvirial

1190 396

1000 Virial 3650 1216

Conclusions• Intermediate sized clusters have

modest effects on disks and planet formation

– FUV flux levels are low enough to leave disks unperturbed

– most interactive system will only truncate disk to rd ~ 200 AU

– disruption of planetary systems is a small effect, bC ~ 700-4000 AU and disruption requires at least 250 AU approach

– ejection rates for encounters with passing cluster members are lower than ejection rates from encounters with planets within the system

• Central concentration and mass segregation play an important role in increasing the interaction rate

Squares: 2 kpc sample, complete down to N = 30 (Lada & Lada 2003)Triangles: 1 kpc sample, complete down to N = 10 (Porras et al. 2003)

Dashed: 1 kpc sample subjected to same selection criteria as the 2 kpc sample