Statistics of multiple stars A.Tokovinin Cerro Tololo Inter-American Observatory

Multiple Star Catalog

Outline Multiple stars are frequent: Many (all?) close binaries are multiple P out – P in : formation + evolution Eccentricities and stability Mass ratios Orbit orientation

True multiplicity: detection?

Hipparcos vs. MSC: FGK stars B-V>0.5 B-V < 1 Exclude giants Distance <50 pc Dist.MSCHIPfract. 8 pc pc pc pc

Hipparcos vs. MSC: N(d) 25% are multiple?

Hipparcos vs. MSC: summary Multiples within 50 pc, FGK type: 76 known, ~700 expected Where do they hide? Visual binaries, CPM… Within 8pc: 4*(C+V), 1*(V+S) Some 15-25% of FGK stars are multiple Sterzik & Durisen (1998): small clusters produce multiples

Radial velocities of visual binaries (Tokovinin & Smekhov 2002) ~1/3 of visual binaries are multiple Sample N syst. Var+SBFraction Orbital visual binaries Wide visual binaries Tertiary components

Close binaries are multiple Duquennoy & Mayor 1991, P<10d: 5 out of 5 are triple SB8, FGK <100pc, P<10d 43% are at least triple Are ALL close binaries triple (because they were formed this way)? VY Ari is not triple?

Distribution of inner periods Low-mass dwarfs

Kozai cycles + tides

Age 2.5 Gyr, masses ( ),( ) solar

Diagram P out - P in Are all those points true?

P out - P in for FGK multiples <50pc

Mon R2 IRS3 (Preibisch et al. 2002)

Formation: cartoon

Formation and P out – P in diagram

P out - P in for young multiples

Important conclusions: Multiple stars form with 7<P out /P in <10000 Dynamics of small-N clusters is the likely formation mechanism? Periods <10d result from tidal dissipation Multiples form within few Myrs

Are triple systems stable? Mardling & Aarseth 2001: (P out /P in ) 2/3 = 2.8 (1 +q) 1/15 (1+e) 0.4 (1-e) -S S=1.2 S=0.9? (Sterzik & Tokovinin) S=2? (reality)

e out : simulated triples Simulated triples (Sterzik & Tokovinin 2002)

e out : real multiples Systems with two known orbits: V+S, V+V, S+S Diamonds: logP out <5 (reliable orb.) logP in >1 (no tides) Kui 93

QS Aql = Kui 93 e out = 0.98?

Real multiples (cont.) P out (1-e out ) 3 P in >5

Spectroscopic binaries in SB8: e-logP P(1-e) 3 P(1-e) 3/2 Why??

q out for FGK multiples <50pc q ~ P -1/3 K=1km/s

q out for all FGK multiples

Relative orientation of orbits Sterzik & Tokovinin 2002

Co-rotation vs. counter-rotation N=135

Conclusions N-body dynamics explains frequency, period ratios and orbit orientation, but not period distribution and eccentricities Close binaries form within multiples Gas and/or accretion is significant?