Centimeter and Millimeter Observations of Very Young Binary and Multiple Systems

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Centimeter and Millimeter Observations of Very
Young Binary and Multiple Systems

• -Orbital Motions and Mass Determination
• -Truncated Protoplanetary Disks
• -The OMC1S Region in Orion

Luis F. Rodríguez
CRyA, UNAM
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ORBITAL MOTIONS IN BINARY AND MULTIPLE PROTOSTARS

• L. Loinard, M. Rodríguez, P. DAlessio
  (CRyAUNAM, 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.
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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

1. Gyrosynchrotron from active stellar magnetosphere
2. Free-free emission from ionized outflows
3. Thermal emission from circumstellar disks

No extinction. However, processes (2) and (3)
produce extended sources. These emissions are not
always present.
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Very Large Array
0.1 resolution at 2 cm
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HEAVILY OBSCURED SOURCES

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

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L1551 IRS5
Ha SII Cont.

• Reipurth Bally 2001
• ESO NTT

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Free-free from ionized outflow dominates cm
range, while thermal emission from dust in disk
dominates mm range
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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)gt0.5 (V/30
  km/s)2 (R/AU)
• We obtain (M/Msun)gt0.1

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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
• gt M 1.2 Msun P 260 yr
• In the main sequence, luminosity will be of order
  1 solar luminosity, while now Lbol is of order 30
  Lsun gt 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 gt 1.7 Msun
• Assuming observed separation is close to true
  separation, P lt 360 yr
• Lbol 13 Lsun

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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 gt 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

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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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CONCLUSIONS OF ORBITAL MOTIONS

• Orbital motions in protostars will provide
  important constraints on the early phases of
  stellar evolution
• We are getting reasonable results, but must
  follow strange cases such as IRAS 16293-2422

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What do we know about protoplanetary disks?

• Radii of 100s of AU in T Tauri stars.
• They last between 2 and 10 million years.
• But little is known about their formation, about
  their earliest stages.
• It can be argued theoretically that the disks
  should start small and grow with time

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The binary disks in L1551 IRS5 are much smaller
than the disks found around T Tauri stars, but
their small size is most likely due to tidal
truncation. Other small disks found are also part
of binary systems
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Anglada et al. (2004)
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IRAS 043682557 L1527 VLA-A 7 mm
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VLA 7 mm
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Detailed modeling of disk allows estimate of
parameters Disk Mass 0.3-0.4 solar masses.
Disk Radius 26 AU.
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B
But
A
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Conclusions on Truncated Protoplanetary Disks

• Given multiplicity in star formation it will be
  hard to find truly isolated protoplanetary disks
  to study their evolution, without the effects of
  companion stars.

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OMC-1S A Cluster in Formation

• SMA and VLA observations of OMC1S part of Ph. D.
  Thesis of Luis Zapata (see his poster).

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Optical image of ODell Doi (2003). OMC-1S is a
region with bolometric luminosity of 10,000
solar luminosities from which many optical
outflows emanate.
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VLA-A 3.6 cm Zapata et al. (2004)
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VLA-B 1.3 cm Hypercompact HII Regions Ionized by
Early B-type stars?
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Higher angular resolution VLA-A observations at
7-mm reveal that at least two of the sources are
close binaries 139-409 and 134-411.
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SMA SiO (5-4)
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Molecular Outflows in OMC-1S

• Highly collimated, young CO outflow.
• Multiple SiO outflows.
• CO and SiO observations complementary the CO
  outflow is not evident in SiO and viceversa.

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The Next Frontiers in Star Formation

• With the availability of the SMA and the future
  construction of other interferometers we will
  start to study star formation with new frontiers
• Binary and multiple star formation
• Star formation in the extremes (very massive
  stars and brown dwarfs)
• Starbursts and cosmological star formation (the
  first stars)