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Ray Jayawardhana University of Toronto Mirza Ahmic, Duy Nguyen, Ivana Damjanov

Multiplicity Among Young Stars and Brown Dwarfs Regional variations? VLM regime Binarity-disk connection?. Ray Jayawardhana University of Toronto Mirza Ahmic, Duy Nguyen, Ivana Damjanov Alexis Brandeker, Marten van Kerkwijk. Multiplicity in the  Cha Cluster(~8 Myr).

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Ray Jayawardhana University of Toronto Mirza Ahmic, Duy Nguyen, Ivana Damjanov

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  1. Multiplicity Among Young Stars and Brown Dwarfs Regional variations? VLM regime Binarity-disk connection? Ray Jayawardhana University of Toronto Mirza Ahmic, Duy Nguyen, Ivana Damjanov Alexis Brandeker, Marten van Kerkwijk

  2. Multiplicity in the  Cha Cluster(~8 Myr) 17 stars imaged with VLT/NACO No binaries wider than 20 AU, even though we could detect any companions > 0.07 MSun Deficit of wide binaries, for example, in comparison to TW Hydrae association: likelihood of being same < 2 x 10-4 Stellar encounters in the present configuration cannot account for this deficit Brandeker, Jayawardhana, Khavari, et al. (2006)

  3. Multiplicity in Chamaeleon I (~2 Myr) * Adaptive optics imaging survey in H and K with NACO on the VLT * Able to detect nearly equal brightness pairs at ~ 6-10 AU, q=0.2 at ~30 AU, and companions down to ~15 MJupiter at wide separations * 135 targets: all known Cha I members bright enough for optical or NIR WFS of NACO * Found a total of 28 binaries and 7 triples 6 out of 11 previously known binaries turned out to be triples 22 new binaries identified no quadruples or higher-order multiples found: contrary to some simulations that produce small groups that later break up Ahmic, Jayawardhana, Brandeker, et al., in prep.

  4. A few examples of Cha I multiple systems Ahmic, Jayawardhana, Brandeker, et al., in prep.

  5. Multiplicity Frequency in Cha I Multiplicity Frequency = (B+T+Q) / (S+B+T+Q) = (28+7)/135 = 26% Companion Star Frequency = (B+2T+3Q) / (S+B+T+Q) = (28 + 2 x 7) / 135 = 31% Dependence of MF on SpT Ahmic, Jayawardhana, Brandeker, et al., in prep.

  6. Multiplicity in the VLM Domain in Cha I • * 26 targets in the 0.02 - 0.2 MSun range • * Only two binaries resolved: q~1, a~20 and 26 AU, no new wide pairs • * Multiplicity frequency = 8 (+17-7 )% • - comparable to Kraus et al. (2005, 2006) results in Taurus & Upper Sco • for a combined sample of 60 young VLMOs, mf = 7 (+10-5 )% • comparable to MF for VLM objects in the field (e.g., Close et al. 2003) • no significant evolution of multiplicity between a few Myr to several Gyr? Jayawardhana, Ahmic, Brandeker, et al. (2007)

  7. Stability of VLM Binaries Jayawardhana, Ahmic, Brandeker, et al. (2007) binding energy (ergs) separation (AU)

  8. Puzzle: about half-dozen wide young VLM binaries are now known (e.g., 2MASS J1101-7732 with a~240 AU DENIS-P J161833-251750 with a~140 AU USCO-160028.4 with a~120 AU Oph 162225-2420515 with a~240 AU) Problem: usually these have been found by chance or in small sample studies rather than in well-defined large multiplicity surveys Solution: either wide VLM binaries are rare or there might be an environmental dependence (Konopacky et al. recently found 5/13 binaries, two of them with a~80-90 AU range, among VLM stars in Taurus)

  9. Disks and Multiplicity:  Cha (~8 Myr) • - 7/9 single stars show IR excess • only 1/6 binaries shows IR excess • - tdisk dissipation ~ 9 Myr for singles • tdisk dissipation ~ 5 Myr for binaries Bouwman et al. (2006) [see Brandeker et al. (2006) for AO imaging] mid-infrared excess

  10. Disks and Multiplicity: Cha I (~2 Myr) 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) % Of <20AU binaries, 4/5 lack IR excess Damjanov, Jayawardhana, Scholz, et al. (2007)

  11. Disks and Multiplicity: Upper Sco VLMOs (~5 Myr) 29 VLM stars and brown dwarfs with Spitzer mid-IR photometry and HST or VLT AO imaging Of 6 with companions, 2 don’t show excess: these are the two tightest binaries at 5 & 10 AU 4 show excess: these have separations in the 12 - 130 AU range Scholz, Jayawardhana, Wood, et al. (2007)

  12. Could there be companions in even tighter orbits (unresolved with AO and HST)?

  13. Radial Velocity Survey of Young Stars * ~4 epochs with MIKE on Magellan * ~75 targets in Cha I and ~130 targets in Taurus Companion Detectability Nguyen et al., in prep.

  14. Examples of Varying RV Nguyen et al., in prep.

  15. Near Future Prospects Comprehensive AO+RV surveys of multiplicity in nearby young SFRs, including the VLM regime, to explore variations (e.g., deficit of wide binaries in Cha: Brandeker et al. 2006) Investigations of a possible connection between disk dissipation and close companions

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