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SiO J=5-4 in the HH211 Protostellar Jet Imaged with the SMA

Observation and analysis of SiO J=5-4 emission in protostellar jet HH211 reveal collimated jet structure aligned with H2 emission, providing insights into outflow launching and dynamics. The SiO jet, well collimated and dense, shows high excitation levels and faster motion compared to CO outflow. The study utilizes high-resolution SiO observations to study the launching mechanism of protostellar outflows.

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SiO J=5-4 in the HH211 Protostellar Jet Imaged with the SMA

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  1. 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.

  2. Launching point < several AU from the star How the outflows are launched and collimated? 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” Outflows from protostars Highly-collimated outflow component ? L1551 IRS5

  3. HH211 — an archetype of outflow with highly-collimated jet Cavity & jet observed in the CO J=2-1 Low-velocity component VLSR = 2.2 – 18.2 km/s Cavity structure • 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 High-velocity component VLSR < 2.2 & > 18.2 km/s Jet-like structure Gueth et al. 1999 with PdBI

  4. HH211 outflow observed with the H2 line McCaughrean et al. 2005

  5. SiO J=5-4 observations with the SMA • SiO J=5-4 217.105 GHz (LSB) • 6 x 6m antennas at extended configuration SiO J=3-2 observations with the NMA - SiO J=3-2 130.2687 GHz (LSB) - 6 x 10m antennas at AB, C, & D configurations

  6. 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

  7. beam: 1.60” x 0.88” P.A. -40.7 deg. SiO J=5-4 jet

  8. beam: 1.49” x 1.30” P.A. -39.7 deg. SiO J=3-2 jet

  9. 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 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?

  10. SiO 5-4 SiO 3-2 SiO 1-0 Chandler & Richer (2001), with the VLA SiO 5-4, 3-2 & 1-0 H2 • 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

  11. red LVG results (preliminary) - X(SiO)~10-7 - TK > 250 - 300 K - n(H2) ~ 0.6 - 1 x 107 cm-3 blue SiO 5-4/3-2 ratio (@ 1.6” x 1.6” resolution) • 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

  12. SiO 5-4 SiO 3-2 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

  13. 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 (> 200 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

  14. The high excitation SiO lines in the submillimeter waveband provide us with the key to understand the launching mechanism of the protostellar outflow

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