1. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 T Tauri Multiple Systems Alexis Brandeker Stockholm Observatory Collaborators: Ray Jayawardhana, René Liseau, Pawel Artymowicz, Joan Najita, Diego Mardones, and Karl Haisch

2. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Why study multiple T Tauri stars? Most star systems are multiple – single stars are in minority Binaries provide dynamical masses of, and distances to, star systems, thereby contributing invaluable constraints on stellar evolution models High spatial resolution needed to avoid confusion, critical for accurate positioning in H-R diagram and evaluating SED

3. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Multiple? 1” Examples:

4. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Multiple! 1” T TauS 18 (in MBM 12) VW Cha Keck AO Keck AO ESO 3.6 AO d~140 pcd~275 pcd~160 pc Duchêne, Ghez, & McCabe 2002, ApJ Brandeker, Jayawardhana, & Najita 2003, AJ Brandeker et al. 2001, ApJL 92 mas 63 mas 100 mas

5. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Multiples indeed T Tauri stars show a multiple frequency significantly exceeding the corresponding frequency among MS field stars (e.g. Duquennoy & Mayor 1991, A&A; Reipurth & Zinnecker 1993, A&A; Duchêne 1999, ApJ; Barsony, Koresko, & Matthews 2003, ApJ; previous talks by Tom Greene and Ralph Launhardt) Proposed explanations: –Sensitivity (Ghez 1996, White & Ghez 2001, ApJ ) –Environment (Duchêne 1999, ApJ; Woitas, Leinert & Köhler 2001, A&A) –Dynamical evolution (ejection), (Reipurth 2000, ApJ; Bate, Bonnell, & Bromm 2002 & 2003, MNRAS)

6. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Companion ejection? Speckle: Koresko 2000, ApJL AO: Köhler, Kasper, & Herbst 2000, IAU200 AO: Duchêne, Ghez, & McCabe 2002, ApJ VLBI: Smith et al. 2003, A&A Loinard, Rodríguez, & Rodríguez 2003, ApJL T Tauri South

7. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Spatial vs. spectral With diffraction limited NIR observations of 8-10 m class telescopes we reach resolutions of 40-50 mas, corresponding to 2-3 AU at 50 pc (distance to TWA), or 6-8 AU at 150 pc. A few AU orbital radius mean a few years orbital period – closing the sensitivity gap to the spectroscopic surveys for binaries and opening for dynamical mass estimates. Brandeker, Jayawardhana, & Najita 2003, AJ ~3 AU, >~ 5 yr

8. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Dynamical mass determination: NTT 045251 + 3016 HST/FGS Steffen et al. 2001, ApJ Orbital motion seen spatially and radially determines: Period 6.91±0.04 yr Major axis 4.8±0.4 AU M 1 = 1.5±0.2 M sun M 2 = 0.8±0.1 M sun Distance 145±9 pc + more...

9. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Recent VLT/NACO imaging of  Cha association 1” VLM companion candidate?  H=4 mag, sep=0.17” Jayawardhana, Haisch, Brandeker, & Mardones (in prep.)

10. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 VLT/NACO contrast sensitivity VLM companion candidate M * =20M J M * =15M J M * =10M J 10 Myr BD models from Baraffe et al. 2003, A&A M * = 5M J

11. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Conclusions Ongoing and future AO & spectral surveys for multiple T Tauri star will firmly establish the mf(sep,age) - down to ~ 20 M J. Within a few years, accurate dynamical mass estimates of a number of PMS stars will provide strong constraints on the theory of star formation and early evolution

12. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Post-processing: Myopic deconvolution VW Cha – Brandeker et al. 2001, ApJL

13. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 Duchêne 1999, ApJ 341:547

14. Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 References Barsony, Koresko, & Matthews 2003, ApJ 591:1064 Bate, Bonnell, & Bromm 2002, MNRAS 336:705 Bate, Bonnell, & Bromm 2003, MNRAS 339:577 Baraffe, Chabrier, Barman, Allard, & Hauschildt. 2003, A&A 402:701 Brandeker, Jayawardhana, & Najita 2003, AJ (in press) Brandeker, Liseau, Artymowicz, & Jayawardhana. 2001, ApJ 561:L199 Duchêne 1999, ApJ 341:547 Duchêne, Ghez, & McCabe 2002, ApJ 568:771 Duquennoy & Mayor 1991, A&A 248:485 Ghez 1996, in Evolutionary Processes in Binary Stars, eds. Wijers, Davies, & Tout, 477 Koresko 2000, ApJ 531:L147 Köhler, Kasper, & Herbst 2000, IAU200 Loinard, Rodríguez, & Rodríguez 2003, ApJ 587:L47 Mamajek, Lawson, & Feigelson 1999, ApJ 516:L77 Mardones, Jayawardhana, Haisch, & Brandeker 2003, ESO prop. 70C-0286A Reipurth 2000, ApJ 120:3177 Reipurth & Zinnecker 1993, A&A 278:81 Smith, Pestalozzi, Güdel, Conway, & Benz 2003, A&A (in press) Steffen, Mathieu, Lattanzi, et al. 2001, ApJ 122:997 White & Ghez 2001, ApJ 556:265 Woitas, Leinert & Köhler 2001, A&A 276:982