SMA and ALMA Observations of a Prototypical Binary Protostellar System L1551 NE

67 Pages·2013·11.43 MB·English

by  Power Mac

SMA and ALMA Observations of
a Prototypical Binary Protostellar System L1551 NE

Infall, Keplerian Circumbinary Disk, and Accretion Streams
Takakuwa Shigehisa (ASIAA),!
Masao Saito (NAOJ / JAO),!
Jeremy Lim (HKU),!
Kazuya Saigo (NAOJ ALMA),!
Tomoyuki Hanawa (Chiba Univ.) et al.!
1. Introduction: Binary Protostellar Formation
A substantial fraction of low-mass stars form as binary systems
(Dunquennoy & Mayor ‘91, Mathieu ‘94).
Compared to single star formation,
binary formation is little understood.
High-dynamic Range Observations of Protostellar Binaries!
are essential.!
!
!・Protostellar Envelope (Infall ?)!
!・Circumbinary Disk (Rotation ?)!
!・Connecting Gas Stream!
!from Circumbinary to Circumstellar Disks ?!
Our Target: L1551 NE
Class I source,!
2nd Brightest in Taurus!
(~ 6 Lsolar)!
Reflection nebula!
Fe II jet Driven by Source A!
! !(Reipurth et al. 00, 02)!
L1551 NE!
Close (~ 70 AU)!
protostellar binary!
SUBARU NIR composite image!
! ! !(Hayashi & Pyo 2009)!
VLA 3.6 cm;!
Reipurth et al. 2002!
2. SMA & ALMA Observations of L1551 NE
SMA
àC18O (3-2; 329.331 GHz)
Resolution: 1.36” × 1.06”
Velocity resolution: 0.37 km s-1
Noise level: ~0.078 Jy beam-1!

ALMA Cycle 0 (Filler Project)
àC18O (3-2), 0.9-mm Continuum
Resolution: 0.72” × 0.36” (Cont. > 80 kl)
: 0.82” x 0.49” (Line)
Velocity resolution: 0.22 km s-1
Noise level: ~2.6 mJy beam-1 (Cont. > 80 kl)!
! ! ! : ~0.016 Jy beam-1 (Line)
3. Results: ALMA 0.9-mm Continuum
Compact Components!
associated with Sources A & B!
) Circumbinary
0 !
``Ring''
.
0
Southern U-shaped Feature!
0
0
Gaps + Western Shell-like Feature!
2
J
!
(

n Local Emission Minima!
o
i
t
a Circumstellar
n Disks
i
l
c
e
114400 AAUU à Circumstellar Disks!
D
+ Circumbinary ``Ring’’!
with ``Gaps’’!
Right ascension (J2000.0)
Total Mass ~0.046 M !
solar
SMA C18O (3-2)
Moment 0 map!
High velocity Low velocity
-2.59 ~ -0.37 km s-1 -0.37 ~ +0.0 km s-1
)
0
0.
0
0
2
J
(
n
o
ati
n )
cli 0
e .
D 0 +0.74 ~ +2.96 km s-1 +0.0 ~ +0.74 km s-1
0
0
2
J
(
280 AU
n
o
i
t
a
n
i
l
c
Right ascension (J2000.0) e
D
~800 AU scale, elongated!
circumbinary feature!
Right ascension (J2000.0)
@High-Velocity à North-South Vel. Grad., along the major axis!
@Low-Velocity à West-East Vel. Grad., along the minor axis!
)0.0002J(
.seR noisnecsathgi
R
l
e
d
o
M
.
s
b
O
χ2 model fitting to the High-Velocity Components
à Keplerian Circumbinary Disk
with (M , i, θ) = (0.8 M , -62°, 167°)
* solar

Obs!
.
s
e
R
Mlodel!
e
d
o
M
.
s
b
O
Res!
Contours!
in steps of 2σ!
See Takakuwa et al. (2012) for details.!
Right ascension (J2000.0)!
Low-Velocity Components
à Infalling Gas toward the Keplerian Circumbinary disk ??
Observed & Model P-Vs along the major and minor axes!
Observations Keplerian Only Model Infall --> Keplerian Model
Major
Keplerian-only model cannot!
4
explain the vel. grad. along the!
2
minor axis, nor the northern!
redshifted component.!
)
c
-2
e
s
c
r Outer Infalling component,!
a
-4
(

n
r ~300 AU!
o
4
i Minor kep
t
i
s v ~0.6 km s-1!
o
P inf
2
No rotation!
Note: v < v
-2
inf free-fall!
@M = 0.8 M !
-4 * solar
4 6 8 4 6 8 4 6 8
LSR Velocity (km s-1)
ALMA C18O (3-2)
à
Even High-Vel. Emission closer to the protobinary
2.7-3.4; 9.8-10.5 km s-1 3.5-4.1; 9.2-9.7 km s-1 4.2-4.7; 8.5-9.1 km s-1
)
0
.
0 140 AU
0
0
2
J
(

n
o
i
t
a
n
i
l
c
e
D
Gray scale: Continuum!
S-shaped features, from the Circumbinary Ring to Source A,!
passing through Source B!
à Accretion Stream ?!!
Comparison with theoretical simulation of
binary accretion
(Ochi et al. 2005; Hanawa et al. 2010)
ALMA OBS.
)
0
.
0
MODEL 0
(ALMA BEAM) 0
2
J
(

n
o
ti
a
n
cli
e
D
MODEL
(0.1 arcsec BEAM)
Right ascension (J2000.0)