1. Disk Disruption in Young Embedded Clusters Eva-Marie Proszkow University of Michigan 18 May 2006 Fred Adams (University of Michigan) Phil Myers (Harvard Smithsonian CfA) Marco Fatuzzo (Xavier University)

2. 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)

3. Virial RatioQ ≡ |K/W| Virial Q = 0.5SubvirialQ = 0.04 Mass Segregation largest star at center of cluster Simulations of Embedded Clusters Cluster Membership Cluster Radius Initial Stellar Density Gas Distribution Star Formation Efficiency0.33 Embedded Epocht = 0–5 Myr Star Formation Epocht = 0-1 Myr

4. Mass Profiles Subvirial Virial Simulationpr0r0 a 100 Subvirial0.690.392 100 Virial0.440.703 300 Subvirial0.790.642 300 Virial0.491.193 1000 Subvirial0.821.112 1000 Virial0.591.963

5. –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 G 0 = 3000 will truncate a circumstellar disk to r d over 10 Myr, where (Adams et al., 2004) Effects of Cluster Radiation on Forming Solar Systems

6. 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 L FUV (N) = 8.20 x 10 35 ergs/s

7. Photoevaporation in the Simulated Clusters Simulationr eff (pc)G 0 meanr med (pc)G 0 median 100 Subvirial0.08066,5000.323359 100 Virial0.11234,3000.387250 300 Subvirial0.12681,0000.5491,550 300 Virial0.18139,0000.687992 1000 Subvirial0.197109,6000.9553,600 1000 Virial0.34835,2001.252,060 Around solar mass stars, FUV radiation will not evaporate enough of the disk to prevent gas giant formation Radial Probability Distributions

8. Closest Approach Distributions Simulation 00  b C (AU) 100 Subvirial0.1661.50713 100 Virial0.05981.431430 300 Subvirial0.09571.711030 300 Virial0.02561.632310 1000 Subvirial0.07241.881190 1000 Virial0.01011.773650 A typical star will experience one encounter with the characteristic impact parameter b C during a 10 Myr time span.

9. 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 

10. Solar System Scattering in Clusters Ejection Rate per Star (for a given mass) Integrate over IMF (normalized to cluster size) Subvirial N=300 Cluster  0 = 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

11. 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) Simulationb C (AU)r d (AU) 100 Subvirial713237 100 Virial1430476 300 Subvirial1030343 300 V irial2310770 1000 Subvirial1190396 1000 Virial36501216

12. 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 r d ~ 200 AU –disruption of planetary systems is a small effect, b C ~ 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

14. 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