Transcript SHELL H II REGIONS IN NGC 6334

ORBITAL MOTIONS IN BINARY AND
MULTIPLE PROTOSTARS
L. F. Rodríguez (IAUNAM, Morelia)
L. Loinard, M. Rodríguez, & P. D’Alessio (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
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 can
or cannot be present.
Very Large Array
0.1” resolution at 2 cm
SOURCES:
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L1551 IRS5
YLW 15
L1527 (= IRAS 04368+2557)
IRAS 16293-2422
T Tauri
L1551
Ha + [SII]
Devine et al. (1999)
Ha
[SII]
Cont.
Reipurth & Bally 2001
ESO NTT
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
Rodríguez et al. 1998
Compact
dust disks
Free-free from
ionized outflow
dominates cm
range, while thermal
emission from dust
in disk dominates
mm range
See Poster 14
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 sola 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 about true
separation, P < 360 yr
• Lbol = 13 Lsun
See poster 2
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
• T Tauri
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
T Tauri: Prototype of its class
T Tauri is triple (Koresko 2000)
Data from Dûchene et al. (2002):
Dûchene et al. (2002)
V = 20 km/s => M > 4 Msun
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
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
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
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
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