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

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.

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?

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.

Very Large Array

0.1” resolution at 2 cm

HEAVILY OBSCURED SOURCES:

• L1551 IRS5

• YLW 15

• L1527 (= IRAS 04368+2557)

• IRAS 16293-2422

H

[SII]

Cont.

Reipurth & Bally 2001

ESO NTT

L1551 IRS5

Free-free from ionized outflow dominates cm range, while thermal emission from dust in disk dominates mm range

L1551 IRS5 VLA-A 2 cm

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

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

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

YLW 15 VLA-A 3.5 cm

1990.41

2002.18

YLW 15

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

L1527 VLA-A 7 mm

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

Up to now, binary systems, what about multiples (i. e. triples)?

• IRAS 16293-2422

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

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

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

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…

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…

Anglada et al. (2004)

IRAS 04368+2557 = L1527

VLA-A 7 mm

VLA 7 mm

Detailed modeling of disk allows estimate of parameters:

Disk Mass= 0.3-0.4 solar masses.

Disk Radius = 26 AU.

But…B

A

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.

OMC-1S: A Cluster in Formation

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

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.

VLA-A 3.6 cm

Zapata et al. (2004)

VLA-B 1.3 cm

Hypercompact HII Regions Ionized by Early B-type stars?

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.

SMA SiO (5-4)

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.

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)