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