Star Formation at High Angular Resolution

1
T Tauri Multiple Systems

• Alexis Brandeker
• Stockholm Observatory
• Collaborators
• Ray Jayawardhana, René Liseau, Pawel Artymowicz,
  Joan Najita, Diego Mardones, and Karl Haisch

2
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
Multiple?
Examples
1
4
Multiple!
1
Duchêne, Ghez, McCabe 2002, ApJ
Brandeker, Jayawardhana, Najita 2003, AJ
Brandeker et al. 2001, ApJL
92 mas
63 mas
100 mas
T Tau
S 18 (in MBM 12)
VW Cha
Keck AO Keck AO ESO 3.6 AO d140
pc d275 pc d160 pc
5
Multiples indeed

• T Tauri stars show a multiple frequency
  significantly exceeding the corresponding
  frequency among MS field stars (e.g. Duquennoy
  Mayor 1991, AA Reipurth Zinnecker 1993, AA
  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, AA)
• Dynamical evolution (ejection), (Reipurth 2000,
  ApJ Bate, Bonnell, Bromm 2002 2003, MNRAS)

6
Companion ejection?
T Tauri South
Loinard, Rodríguez, Rodríguez 2003, ApJL

• Speckle Koresko 2000, ApJL
• AO Köhler, Kasper, Herbst 2000, IAU200
• AO Duchêne, Ghez, McCabe 2002, ApJ
• VLBI Smith et al. 2003, AA

7
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.

3 AU, gt 5 yr
Brandeker, Jayawardhana, Najita 2003, AJ
8
Dynamical mass determinationNTT 045251 3016

• Orbital motion seen spatially and radially
  determines
• Period 6.910.04 yr
• Major axis 4.80.4 AU
• M1 1.50.2 Msun
• M2 0.80.1 Msun
• Distance 1459 pc
• more...

HST/FGS Steffen et al. 2001, ApJ
9
Recent VLT/NACO imaging ofh Cha association
1
VLM companion candidate? DH4 mag, sep0.17
Jayawardhana, Haisch, Brandeker, Mardones (in
prep.)
10
VLT/NACOcontrast sensitivity
VLM companion candidate
M20MJ
M15MJ
M10MJ
M 5MJ
10 Myr BD models from Baraffe et al. 2003, AA
11
Conclusions

• Ongoing and future AO spectral surveys for
  multiple T Tauri star will firmly establish the
  mf(sep,age) - down to 20 MJ.
• 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
Post-processing Myopic deconvolution

• VW Cha Brandeker et al. 2001, ApJL

13
Duchêne 1999, ApJ 341547
14
References

• Barsony, Koresko, Matthews 2003, ApJ 5911064
• Bate, Bonnell, Bromm 2002, MNRAS 336705
• Bate, Bonnell, Bromm 2003, MNRAS 339577
• Baraffe, Chabrier, Barman, Allard, Hauschildt.
  2003, AA 402701
• Brandeker, Jayawardhana, Najita 2003, AJ (in
  press)
• Brandeker, Liseau, Artymowicz, Jayawardhana.
  2001, ApJ 561L199
• Duchêne 1999, ApJ 341547
• Duchêne, Ghez, McCabe 2002, ApJ 568771
• Duquennoy Mayor 1991, AA 248485
• Ghez 1996, in Evolutionary Processes in Binary
  Stars, eds. Wijers, Davies, Tout, 477
• Koresko 2000, ApJ 531L147
• Köhler, Kasper, Herbst 2000, IAU200
• Loinard, Rodríguez, Rodríguez 2003, ApJ 587L47
• Mamajek, Lawson, Feigelson 1999, ApJ 516L77
• Mardones, Jayawardhana, Haisch, Brandeker 2003,
  ESO prop. 70C-0286A
• Reipurth 2000, ApJ 1203177
• Reipurth Zinnecker 1993, AA 27881
• Smith, Pestalozzi, Güdel, Conway, Benz 2003,
  AA (in press)
• Steffen, Mathieu, Lattanzi, et al. 2001, ApJ
  122997