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VLBA Orbits of Young Binary Stars

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

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VLBA Orbits of Young Binary Stars

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  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 • d = 145 ± 2 pc • 1.4% error • d = 146 ± 0.6 pc • 0.4% error 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 = 93+115-55 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 Keck Interferometer (Boden et al. 2007) VLBI (Phillips, 1996, Boden et al. 2007) VLBA RV RV RV In the reference frame of V773 Tau Aa 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 6 observations over 1 year 13 observations over 1 orbital period (~ 52 days) 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

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