zurück zur ersten seite dynamical decay of young few-body clusters and “isolated“ t tauri stars...

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Dynamical Decay of Young

Few-Body Clusters and “Isolated“ T Tauri Stars

Michael Sterzik, ESO

Richard Durisen, Indiana University

Brian Pickett, Valparaiso University

Scenario: Disintegrating Multiples in Early Stellar Evolution Results and Predictions of Numerical Simulations Are there “Isolated“ TTS? “Run-Away“ TTS? Ejected BDs?

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Core Fragmentation: Observations

Molecular Cloud Cores fragment down to scales of <0.1pcCore mass spectrum resembles stellar IMF

Andre et al., 2000, Protostars and Planets IVSerpens core: Testi & Sargent, 2000, ApJL

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Fragmentation during Cloud Collapse

During 1st (isothermal) collapse MJ Msol

RJ 100 - 1000 A.U. difficult in spherical, centrally

condensed cores, but: prolate cores with gaussian, or

uniform, profiles fragment ! simulations:

Bonnell, Boss, Burkert, Bodenheimer, Nelson, Monaghan, Klein, Sigalotti

Phases of cloud collapse

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Scenario

system scale 0.1 pc

300AU

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Example: Burrau‘s problem „Pythogorean“ 3 body

problem (Burrau 1913) Solution by Szebehely &

Peters (1967)

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Burrau‘s problem with CHAIN

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Qualitative features of disintegratingfew-body systems

Lifetime: tens of crossing times (Tcr = GMtot 5/2 / E0 3/2)

Encounters cause energy redistiribution: tight subsystems and escapers

Remnant binaries consists of most massive bodies („dynamical biasing“), rel. high eccentricity

Escapers are single, and less massive Formation of very close binaries rare Higher-order systems are hierarchically organized

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Physical Scaling

- Etot/M tot = const. vvir = const.- Rvir = 125 AU and Mtot = 3M : vvir = 3.3 km/sec

Dispersion Velocities

HUGE differences in recoil velocities of S and B‘s dispersion velocities can be significant >vvir

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System Scale and Binary Separation Distributions

post-collapse separation distribution broadened post-collapse scale reduced by 5-10 BSD depend on primary mass tends to agree (qualitatively) with DM !

Initial meanSeparations

Final BinarySeparationDistribution

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Application: variation of IMF(Sterzik & Durisen 1995, 1998, 1999; Durisen, Sterzik, Pickett 2000, 2001)

Initial condition: N=4, spherical, cold (==0) compare „two-step“ IMFs incl BDs (stellar MF is drawn from a

clump MF) CMS4-BDstd CMS4-BDenh

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Single and Binary fractionsadopted mass binning: F+ (m > 1.2M ) KG (0.5M < m < 1.2M ) MK (0.2M < m < 0.5M ) M (0.075M < m <0.2M ) L (m < 0.075M )

CMS4-BDstd

CMS4-BDenh

F+ KG MK M L F+ KG MK M L

Single Fractions

3% 14% 51% 96% 100% 76% 66% 39% 3% 0%

.3% 9% 44% 98% 99.6% 85% 76% 44% 2% .4%

Binary Fractions

Duquennoy & Mayor 1991 57+-9%Fischer & Marcy 1992 42+-9%Leinert et al. 1997 26+-9%*Abt et al. 1990 >80%*** see Delfosse et al. 1999 for additional detections** B2-B5

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Spatial Evolution of a loose Cluster

Initial star formation volume (RSFR = 10pc) Continuous star formation rate (10 Msol/My) Populate with results from decay calcs Propagate locations according to system velocities Compare with fiducial gaussian vel. distribution

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Fiducial Few-Body Decay

„Kinematical Relaxation“: B and T segregate from S and bd„isolated“ run-away stars are preferentially S and low-mass

Symbol size = log(System mass) Single Binary Triple browndwarf

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Where are raTTS / isolated TTS?

GJ 117

t= -30 Myr

t= -20 Myr

t= -10 Myr

t= 0

GJ 182

BD +224409

t= -10 Myr

t= -20 Myr

The large scale spatial distribution of ROSAT selected young stellar candidates in Orion

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Protostellar Jets... Multiplicity in HH111: decaying triple system

(Reipurth et al, 1999, A&AL)

highest BF in sources of giant HH flows HH activity related to binary orbit modulation? IRC binaries (!), accompanied by visible TTS TMR-1C: „ejected protoplanet“ (Terebey et al. 1998, Petr, Cuby,

Sterzik, 2000)

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Conclusions few-body decay is likely in early stellar evolution stellar dynamics approximates the evolution two-step IMF can reproduce obsvd. trends in BF & MR cluster decay broadens and reduces scale by 10 velocity distributions are nonGaussian, high vel. Tails spatial segregation of multiples from singles field brown dwarfs are single, with significant velocities

Star formation during a paradigm shift from binary to multiple star formation