Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 T Tauri Multiple Systems Alexis Brandeker Stockholm Observatory Collaborators:

Star Formation at High Angular Resolution

IAU Symposium 221, Sydney 2003

T Tauri Multiple SystemsT Tauri Multiple Systems

Alexis BrandekerStockholm Observatory

Collaborators:

Ray Jayawardhana, René Liseau, Pawel Artymowicz, Joan Najita, Diego Mardones, and

Karl Haisch



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



Multiple?

1”

Examples:



Multiple!

1”

T Tau S 18 (in MBM 12) VW Cha Keck AO Keck AO ESO 3.6 AO d~140 pc d~275 pc d~160 pc

Du

ch

ên

e,

Gh

ez,

& M

cC

ab

e 2

00

2,

Ap

J

Bra

nd

eker,

Jayaw

ard

han

a,

& N

ajita

20

03

, A

J

Bra

nd

eker

et

al.

20

01

, A

pJL

92 mas63 mas 100 mas



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)



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 SouthT Tauri South



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



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

• M1 = 1.5±0.2 Msun

• M2 = 0.8±0.1 Msun

• Distance 145±9 pc• + more...



Recent VLT/NACO imaging of

Cha association

1” VLM companion candidate?H=4 mag, sep=0.17”

Jayawardhana, Haisch, Brandeker, & Mardones (in prep.)



VLT/NACOcontrast sensitivity

VLM companion candidate M

*=20MJ

M*=15MJ

M*=10MJ

10 Myr BD models from Baraffe et al. 2003, A&A

M*= 5MJ



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



Post-processing: Myopic deconvolution

VW Cha – Brandeker et al. 2001, ApJL



Duchêne 1999, ApJ 341:547



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

Documents

Star Formation at High Angular Resolution IAU Symposium 221, Sydney 2003 T Tauri Multiple Systems Alexis Brandeker Stockholm Observatory Collaborators: