Diapositiva 1

1
VLBA Orbits of Young Binary Stars
Rosa M. Torres CRyA, UNAM Laurent Loinard
CRyA, UNAM Amy Mioduszewski DSOC, NRAO Luis
F. Rodríguez CRyA, UNAM Andy Boden Caltech
2
Introduction
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
3
Taurus
L.Loinard talk last Tuesday
Torres et al. 2009
30 pc
d 160 pc
29 pc
d 140 pc
d 130 pc
36 pc
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
4
Parallax with VLBA

• Phase referencing
• Continuum mode at 8.42 GHz
• Observations every 2 or 3 months
• More frequently for orbits
• PMS stars (not masers) in Taurus Ophiuchus
• Low mass and magnetic
• Compact and bright sources
• We detect non-thermal emission coming from
  stellar magnetospheres
• Gyrosyncrotron emission

B 1 G E 1 MeV
www.nrao.edu
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
5
T Tau
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
6
T Tau system
12 observations
TTau system with NACO in the Ks photometric band
on 2006 Oct. 11 (Köhler et al. 2008)
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
7
Astrometry

• Initial position ? at some epoch (usually 2000)
• Angular velocity ? the proper motions
• Parallax ? with the projection of the equation of
  the ellipse over the axis of coordinates
• Angular acceleration (uniform)

a(t) aJ2000.0 mat ½ aat2 p
fa(a,d,t) d(t) dJ2000.0 mdt ½ adt2 p
fd(a,d,t)
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
8
Proper motion
Loinard et al. 2007
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
9
Proper motion
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
10
Previous orbit
Fit by Köhler et al. (2008) P 93115-55 yr
Fit by Dûchene et al. (2006) P 21.66 0.93 yr

• Near IR
• VLBA

Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
11
Our orbit
P 25.83 7.9 yr
T Tau Sa
T Tau Sb
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
12
V773 Tau
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
13
V773 Tau system
A. Boden talk last Tuesday

• Brightest radio source in Taurus
• The first multiple system to display such a
  variety of evolutionary states

19 observations
V773 Tau A Spectroscopic binary T Tauri
Weak-Line Period of 52 days
V773 Tau B Visual companion Classical T Tauri at
0.1 arcsec
V773 Tau C IR companion at 0.2 arcsec
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
14
First six observations
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
15
Orbit
A. Boden talk last Tuesday
Boden et al. 2007
Torres et al. 2009
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
16
Physical parameters

• Keck VLBA ? dynamical masses and distance
• MAa 1.48 0.12 Msun
• MAb 1.28 0.07 Msun
• d 134.6 3.6 pc
• VLBA ? distance
• d 134.8 3.8 pc
• Photometry IR ? magnitude
• Spectral ? temperature
• ? ? HR diagram ? ages

luminosity
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
17
Comparison with models
A. Boden talk last Tuesday
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
18
Flux evolution 19 epochs
13 observations over 1 orbital period ( 52 days)
6 observations over 1 year
The dotted lines show the periastron passages
assuming as a initial epoch t0 2449330.94 JD
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
19
Total intensity
(each panel 1 epoch)
from epoch 7 to epoch 19
Average Each hour
Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009
20
Conclusions

• V773 Tau AB suggest that the emitted flux is a
  function of the separation between the two stars
• Accurate orbit determination for PMS binaries
• Dynamical masses
• Constrain PMS evolutionary models
• Observations of the structure of the stars at
  higher resolution reveal variation in the
  structure of the active magnetosphere

Rosa M. Torres New Science Enabled by
Microarcsecond Astrometry Socorro, NM July
23, 2009