ORBITAL MOTIONS IN BINARY AND MULTIPLE PROTOSTARS

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ORBITAL MOTIONS IN BINARY AND MULTIPLE PROTOSTARS

• L. F. Rodríguez (IAUNAM, Morelia)
• L. Loinard, M. Rodríguez, P. DAlessio
  (IAUNAM, Morelia)
• S. Curiel, J. Cantó, A. C. Raga (IAUNAM, México
  City)
• J. M. Torrelles (IEEC, Spain), J. M. Girart (U.
  Barcelona, Spain)
• David J. Wilner Paul T. P. Ho (CfA, USA)

High angular resolution (0.1) Very Large Array
observations of young stellar systems that allow
measurement of orbital proper motions and
estimate of stellar masses.
Union of two fields where Arcadio Poveda has made
significant contributions
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BACKGROUND

• Most information on stellar masses comes from
  studies of orbital motions
• Work at optical band toward visible stars has
  been going on for 200 years
• In the last decade, near-IR speckle and adaptive
  optics has been used to investigate T Tauri
  binaries
• What about heavily obscured protostars, not
  detectable even at near-IR wavelengths?

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RADIO OBSERVATIONS

• Remarkably, protostars can be tracked at radio
  wavelengths due to three processes

• Gyrosynchrotron from active stellar magnetosphere
• Free-free emission from ionized outflows
• Thermal emission from circumstellar disks

No extinction. However, processes (2) and (3)
produce extended sources. These emissions can or
cannot be present.
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Very Large Array
0.1 resolution at 2 cm
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SOURCES

• L1551 IRS5
• YLW 15
• L1527 ( IRAS 043682557)
• IRAS 16293-2422
• T Tauri

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L1551 Ha SII Devine et al. (1999)
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Ha SII Cont.

• Reipurth Bally 2001
• ESO NTT

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L1551 IRS5

• Near-IR source (Strom et al. 1976) that excites
  bipolar flow (Snell et al. 1980)
• Located at Taurus at 140 pc
• Bolometric luminosity of 30 Lsun
• Embedded in dense core (1000 AU)
• Believed to be single star, now it is known to be
  a binary system

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Rodríguez et al. 1998
Compact dust disks
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Free-free from ionized outflow dominates cm
range, while thermal emission from dust in disk
dominates mm range
See Poster 14
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L1551 IRS5 VLA-A 2 cm
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Proper Motions

• Large proper motions due to large scale motion of
  region with respect to Sun and agree very well
  with Jones Herbig (1979)
• However, proper motions not identical for N and S
  components, indicating relative (orbital) motions

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Orbital Proper Motions

• Observed changes in separation and position angle
  imply relative velocity in the plane of the sky
  of 2.3-0.5 km/s
• A (very) conservative lower limit to the total
  mass can be derived from (M/Msun)0.5 (V/30
  km/s)2 (R/AU)
• We obtain (M/Msun)0.1

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An attempt to correct for projection effects...

• Assume plane of orbit parallel to plane of disks
  (Bate et al. 2000)
• Circular orbit
• M 1.2 Msun P 260 yr
• In the main sequence, luminosity will be of order
  1 sola luminosity, while now Lbol is of order 30
  Lsun accretion main source of luminosity

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YLW 15 VLA-A 3.5 cm
1990.41
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2002.18
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YLW 15
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YLW 15

• Relative velocity in the plane of the sky of
  6.4-1.8 km/s, implying
• M 1.7 Msun
• Assuming observed separation about true
  separation, P
• Lbol 13 Lsun

See poster 2
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L1527 VLA-A 7 mm
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Relative Velocity in Plane of the Sky 4-2
km/s M 0.1 Msun, most likely 0.5 Msun Lbol
about 2.5 Lsun
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Up to now, binary systems, what about multiples
(i. e. triples)?

• IRAS 16293-2422
• T Tauri

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IRAS 16293-2422, VLA-A, 3.5 cm, average proper
motion subtracted
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IRAS 16293-2422

• Relative velocity of about 15 km/s and separation
  of about 30 AU between components A1 and A2,
  implies relatively large mass of about 4 Msun
• However, A1 has been proposed in the past to be
  shock with ambient medium

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T Tauri Prototype of its class
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T Tauri is triple (Koresko 2000)Data from
Dûchene et al. (2002)
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Dûchene et al. (2002)
V 20 km/s M 4 Msun
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What are we seeing in the radio?

• Comparison between radio and near-IR, as well as
  circular polarization characteristics of southern
  source indicates that in the radio we are always
  seeing T Tau Sb
• Even when in the radio we do not see component
  Sa, it is possible, combining radio and near-IR
  to obtain orbit of Sb relative to Sa
• This relative orbit comes from detailed
  astrometric measurements and corrects for
  relative motion of Sa with respect to N

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What makes us think the orbit changed?

• Last two points do not fit previous ellipse
• Area/time for last two points larger than for
  previous points
• Large mass (4 Msun) required for bound motions,
  while 2 Msun required before 1995

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Arguments against

• Something may be wrong with measurements
• Suggested ejection very unlikely, although
  evidence for ejections exists in literature
  (Allen et al. 1974 Hoogerwert et al. 2000)
• Johnston et al. (2003) model all data points with
  a single ellipse

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Future observations will solve the issue

• We are undertaking new radio and near-IR
  observations to follow motion of T Tau Sb
• In this scheme of orbital change (or even
  ejection or escape), T Tau Sa must be a binary,
  making the T Tauri system a quadruple

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CONCLUSIONS

• Orbital motions in protostars will provide
  important constraints on the early phases of
  stellar evolution
• We are getting reasonable results, but must
  follow cases of IRAS 16293-2422 and T Tauri
• Now we are limited by modest signal-to-noise
  ratio, but this situation will greatly improve
  with EVLA, ALMA, and SKA