SiO J=5–4 in the HH211 protostellar jet imaged with the SMA

We have mapped the SiO J=5–4 line at 217GHz from the HH2̇11 molecular outflow with the Submillimeter Array (SMA). The high resolution map (1.6×0.9) shows that the SiO J=5–4 emission comes from the central narrow jet along the outflow axis with a width of ∼0.8 (∼ 250AU) FWHM. The SiO jet consists of a chain of knots separated by 3–4 (∼ 1000AU) and most of the SiO knots have counterparts in shocked H2 emission seen in a new, deep VLT near-infrared image of the outflow. A new, innermost pair of knots are discovered at just ±2 from the central star. The line ratio between the SiO J=5–4 data and upper limits from the SiO J=1–0 data of Chandler & Richer (2001) suggests that these knots have a temperature in excess of 300–500K and a density of (0.5–1)×10 cm. The radial velocity measured for these knots is ∼ 30 km s, comparable to the maximum velocity seen in the entire jet. The high temperature, high density, and velocity structure observed in this pair of SiO knots suggest that they are closely related to the primary jet launched close to the protostar. Subject headings: ISM: individual (HH211) — ISM: jets and outflows — ISM: molecules — shock waves—stars: formation Academia Sinica, Institute of Astronomy & Astrophysics, P.O. Box 23–141, Taipei, 106, Taiwan, R.O.C. e-mail: [email protected] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Department of Earth Science, National Taiwan Normal University, 88 Sec. 4, Ting-Chou Rd., Taipei, 116, Taiwan, R.O.C. School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, Devon, UK