SiO J=5-4 in the HH211 Protostellar Jet

Imaged with the SMA

Naomi Hirano (ASIAA, Taiwan)(=^_^=)(=^_^=)/

Sheng-yuan Liu1, Hsien Shang1, PaulT.P. Ho2, Hui-Chun Huang3, Yi-Jehng Kuan1,3, Mark McCaughrean4, & Q. Zhang2

1. ASIAA, Taiwan, 2. CfA, U.S.A., 3. NTNU, Taiwan, 4. U. of Exeter, U.K.

Outflows from protostars

L1551 IRS5

How the outflows arelaunched and collimated?

Highly-collimated outflow component

An important link between the primary jet & entrained flow?

CO outflow ≠ directly ejected material–ambient gas swept-up and entrained by the “unseen primary jet”

Launching point

< several AU from the star

?

Cavity & jet observed in the CO J=2-1

Gueth et al. 1999 with PdBI

Low-velocity component VLSR = 2.2 – 18.2 km/sCavity structure

High-velocity component VLSR < 2.2 & > 18.2 km/sJet-like structure

HH211 — an archetype of outflow with highly-collimated jet

• Highly-collimated outflow

(aspect ratio ~ 15:1)

• Driven by the low-luminosity

(3.6 Lo) Class 0 protostar

(Tbol ~ 33 K)

• Dynamical time scale ~ 750 yr

• Outflow axis ~ 10° from the plane of the sky

HH211 outflow observed with the H2 line

McCaughrean et al. 2005

SiO J=5-4 observations with the SMA

SiO J=3-2 observations with the NMA

•SiO J=5-4 217.105 GHz (LSB)

•6 x 6m antennas at extended configuration

- SiO J=3-2 130.2687 GHz (LSB)

- 6 x 10m antennas at

AB, C, & D configurations

Why SiO?

•SiO emission is barely seen in the cold dark clouds–Si/C ~ 1/10

–SiO/CO < 10-8 in TMC1

–SiO is heavily depleted onto the dust grain

•SiO is a good tracer of shocked molecular gas–Si or SiO is librated into the gas phase because

of shock wave

–SiO abundance is increase by several orders of magnitude

SiO J=5-4 jet

beam: 1.60” x 0.88” P.A. -40.7 deg.

Max: 2.09 Jy/beam <--> TB ~ 153.8 K

SiO J=3-2 jet

beam: 1.49” x 1.30” P.A. -39.7 deg.

Max: 0.62 Jy/beam <--> TB ~ 93 K

Characteristics of the SiO jet

• The SiO jet is well collimated, and perfectly aligned with the knots seen in the shocked H2

➡ The SiO jet is closely linked with the H2 jet

• No cavity component

• No SiO emission beyond ±20”

➡ Dense (> 105 - 106 cm-3) & warm (> 150 K) jet is running along the axis of the low density cavity

• The SiO jet consists of a chain of knots separated by 3-4” (~1000 AU)

➡ Non-steady eruption?

SiO 5-4, 3-2 & 1-0

• Higher transition of the SiO is better collimated and strong in the vicinity of the protostar

• The innermost knot pair (related to the latest activity) is seen only in the maps of higher transitions of SiO

SiO 5-4

SiO 3-2

SiO 1-0

Chandler & Richer (2001), with the VLA

H2

SiO 5-4/3-2 ratio

• SiO 5-4/3-2 line ratio is hign (~2) at the upstream and decreases toward the downstream

• High 5-4/3-2 ratio is seen along the flow axis

red

blue

(@ 1.6” x 1.6” resolution)

LVG results(preliminary)

- X(SiO)~10-7

- TK > 250 - 300 K- n(H2) ~ 0.6 - 1 x 107 cm-3

Position-velocity map along the major axis

• Steep velocity gradient between the star and the innermost knots

• ±18 km/s at ±2” (~ 630 AU)

• dynamical age of the innermost knots < 175 yr

• The SiO jet is moving faster than the CO 2-1 jet

• – V(SiO ) ~ V(CO)+5 km/s

SiO 5-4 SiO 3-2

Summary• The SiO jet is perfectly aligned with the H2 jet

• The SiO 5-4 & 3-2 traces the dense (> 106 cm-3) and warm (> 150 K) jet running along the axis of the low-density cavity

• The excitation condition of the SiO jet varies along the radial and axial direction (SiO 5-4/3-2 ratio, SiO 5-4, 3-2, & 1-0 maps)

• The dense and warm jet component with higher velocity (traced by the SiO) is surrounded by the less dense cold, and lower-velocity component (traced by the CO)

• The innermost pair of knots at 2” from the source are first discovered with the SiO 5-4 and 3-2.

• - High excitation & high velocity --> these knots are closely linked to the primary jet

The high excitation SiO lines in the submillimeter waveband provide us with

the key to understand the launching mechanism of the protostellar outflow