Multiplicity in the Chamaeleon I SFR

1. Multiplicity in the Chamaeleon I SFR Mirza Ahmic University of Toronto Ray Jayawardhana, Alexis Brandeker, Aleks Scholz, Ivana Damjanov, Marten van Kerkwijk

2. Multiplicity properties important to constrain formation mechanisms of stars and brown dwarfs Ejection In situ Might also leave clues to identifying regions where most stars form Multiplicity rate in denser stellar clusters (such as Orion Trapezium) in agreement with field Least dense T associations show a factor of ~2 multiplicity excess Higher order systems can be used to constrain evolutionary models White et al. (1999) - GG Tau Konopacky et al. (2007) – TWA5 Motivation Luhman et al. 2006

3. 135 Targets Imaged 28 objects with SpT>M5.5 2 and 9 previously known triples and binaries Observations carried out with VLT NAOS-CONICA (NACO for short) CONICA has a high resolution lens (13.26mas/pixel) resulting in a 13.6”X13.6” FOV IR H (1.66µm) and Ks(2.18µm) filters Chamaeleon I SFR Survey

4. Multiplicity in the Chamaeleon I SFR • Survey sensitive enough to detect: • Equal mass binaries down to separations of 0.04-0.07” (~6-10AU) • Typically companions with mass ratios (q=m1/m2) as low as 0.2 outside of 0.2” (30AU) for the VLMO, even smaller for stars • Found a total of 28 binaries and 7 triples • 5 out of 9 previously known binaries turned out to be triples • 22 new binaries identified • no quadruples or higher-order multiples found Ahmic et al., in prep.

5. Binaries

6. Higher-Order Multiples I

7. Higher-Order Multiples II

8. Higher-Order Multiples III

9. Comparison with Simulations • MF = 0.26 • CSF = 0.31

10. Multiplicity Evolution • No quadruples or higher order systems • Only one unstable triple • Very few higher order systems • Only 20% of multiples are triples • 83% and 39% at 0.5Myr and 10.5Myr (Delgado-Donate et al. 2004) • 56% at 0.3Myr(Goodwin et al. 2005) • Likely no evolution • But… should combine results with a spectroscopic survey to rule out additional close companions to the multiples

11. Multiplicity vs. Mass

12. VLM Regime Jayawardhana et al. (2007)

13. VLM Binary Frequency and Mass Dependence • 3 binary systems out of 28 observed targets • 11+17-9% • Combined with Kraus et al. (2005,2006) and Konopacky et al. (2007) surveys of Taurus and Upper Scorpius (q>0.85, >7.5AU) • 5/72, 7+9-4% • 3/85, 4+6-4% (Burgasser et al. 2003; Close et al. 2003; Siegler et al. 2005) • MF mass dependence also evident in the VLM regime • 0/27 for M*<70MJ vs. 5/45 for M*>70MJ

14. Multiplicity – Disk Connection • 63 stars and BDs with Spitzer mid-IR fluxes and VLT AO imaging • Of those, 15 binaries and 2 triples • disk frequency among binaries: 35+15-13% • Disk frequency among singles: 46+9-9% • Of <20AU binaries, 4/5 lack IR excess • Of <50AU, binaries, 9/12 lack IR excess Damjanov et al. (2007)

15. Summary • Surveyed 135 objects (B6 to M8) • Complete down to K~11.0 • Resolved 35 multiples • 28 binaries (22 new), 7 triples (5 new) • Only 1 non-hierarchical triple and no higher order multiples, suggesting break up of higher order multiples is not a viable channel for multiplicity evolution • 3 VLMO binaries, all with separations >20AU, 0.64<q<0.95 • MF mass dependence extends to the VLM regime • Binary frequency comparable to the field • Connection between disks and multiples