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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. D’Alessio (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 04368+2557)
• IRAS 16293-2422
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H
[SII]
Cont.
Reipurth & Bally 2001
ESO NTT
L1551 IRS5
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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)>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 solar 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 is close to true separation, P < 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 > 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 04368+2557 = 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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But…B
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 O´Dell & 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)