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. 2 Introduction Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009

3. 3 d = 160 pc d = 140 pc d = 130 pc 30 pc 29 pc 36 pc Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Taurus Torres et al. 2009 L.Loinard talk last Tuesday

4. 4 B~ 1 G E ~ 1 MeV www.nrao.edu 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 Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Parallax with VLBA

5. 5 T Tau Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009

6. 6 TTau system with NACO in the K s photometric band on 2006 Oct. 11 (Köhler et al. 2008) Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 T Tau system 12 observations

7. 7 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)  (t) =  J2000.0 +   t + ½ a  t 2 +  × f  ( , ,t)  (t) =  J2000.0 +   t + ½ a  t 2 +  × f  ( , ,t) Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Astrometry

8. 8 d = 145 ± 2 pc 1.4% error d = 146 ± 0.6 pc 0.4% error Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Proper motion Loinard et al. 2007

9. 9 Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Proper motion

10. 10 Near IR VLBA Fit by Dûchene et al. (2006) P = 21.66 ± 0.93 yr Fit by Köhler et al. (2008) P = 93 +115 -55 yr Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Previous orbit

11. 11 P = 25.83 ± 7.9 yr T Tau Sa T Tau Sb Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Our orbit

12. 12 V773 Tau Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009

13. 13 Brightest radio source in Taurus The first multiple system to display such a variety of evolutionary states V773 Tau B Visual companion Classical T Tauri at 0.1 arcsec V773 Tau C “IR companion” at 0.2 arcsec V773 Tau A Spectroscopic binary T Tauri Weak-Line Period of 52 days Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 V773 Tau system 19 observations A. Boden talk last Tuesday

14. 14 Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 First six observations

15. 15 Boden et al. 2007 RV Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Orbit VLBI (Phillips, 1996, Boden et al. 2007) VLBA Keck Interferometer (Boden et al. 2007) In the reference frame of V773 Tau Aa A. Boden talk last Tuesday Torres et al. 2009

16. 16 Keck + VLBA  dynamical masses and distance –M Aa = 1.48 ± 0.12 M sun –M Ab = 1.28 ± 0.07 M sun –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. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Physical parameters

17. 17 Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Comparison with models A. Boden talk last Tuesday

18. 18 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 t 0 = 2449330.94 JD Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Flux evolution 19 epochs

19. 19 from epoch #7 to epoch #19 (each panel = 1 epoch) Average Each hour Rosa M. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Total intensity

20. 20 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. TorresNew Science Enabled by Microarcsecond Astrometry Socorro, NM – July 23, 2009 Conclusions