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

2. Multiple Star Catalog

3. Outline Multiple stars are frequent: 0.15-0.25 Many (all?) close binaries are multiple P out – P in : formation + evolution Eccentricities and stability Mass ratios Orbit orientation

4. True multiplicity: detection?

5. Hipparcos vs. MSC: FGK stars B-V>0.5 B-V < 1 Exclude giants Distance <50 pc Dist.MSCHIPfract. 8 pc5180.28 15 pc111120.10 20 pc182520.07 50 pc7633830.02

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

7. 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 0.15-0.35 multiples

8. Radial velocities of visual binaries (Tokovinin & Smekhov 2002) ~1/3 of visual binaries are multiple Sample N syst. Var+SBFraction Orbital visual binaries 177520.29 Wide visual binaries 26120.46 Tertiary components 59180.30

9. 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?

10. Distribution of inner periods Low-mass dwarfs

11. Kozai cycles + tides

12. Age 2.5 Gyr, masses (1.4+1.3),(1.3+1.2) solar

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

14. P out - P in for FGK multiples <50pc

15. Mon R2 IRS3 (Preibisch et al. 2002)

16. Formation: cartoon

17. Formation and P out – P in diagram

18. P out - P in for young multiples

19. 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

20. 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)

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

22. 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

23. QS Aql = Kui 93 e out = 0.98?

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

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

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

27. q out for all FGK multiples

28. Relative orientation of orbits Sterzik & Tokovinin 2002

29. Co-rotation vs. counter-rotation N=135

30. 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?