We observed the HH 211 jet in the submillimeter continuum and the CO ( 3–2 ) and SiO ( 8–7 ) transitions with the Submillimeter Array .
The continuum source detected at the center of the outflow shows an elongated morphology , perpendicular to the direction of the outflow axis .
The high-velocity emission of both molecules shows a knotty and highly collimated structure .
The SiO ( 8–7 ) emission at the base of the outflow , close to the driving source , spans a wide range of velocities , from -20 up to 40 km s ^ { -1 } .
This suggests that a wide-angle wind may be the driving mechanism of the HH 211 outflow .
For distances \geq 5 ^ { \prime \prime } ( \sim 1500 AU ) from the driving source , emission from both transitions follows a Hubble-law behavior , with SiO ( 8–7 ) reaching higher velocities than CO ( 3–2 ) , and being located upstream of the CO ( 3–2 ) knots .
This indicates that the SiO ( 8–7 ) emission is likely tracing entrained gas very close to the primary jet , while the CO ( 3–2 ) is tracing less dense entrained gas .
From the SiO ( 5–4 ) data of Hirano et al .
we find that the SiO ( 8–7 ) /SiO ( 5–4 ) brightness temperature ratio along the jet decreases for knots far from the driving source .
This is consistent with the density decreasing along the jet , from ( 3–10 ) \times 10 ^ { 6 } cm ^ { -3 } at 500 AU to ( 0.8–4 ) \times 10 ^ { 6 } cm ^ { -3 } at 5000 AU from the driving source .