Kinematics of SiO J = 8 - 7 Emission towards the HH 212 Jet

We present SiO J=8-7 (347.3 GHz) observations towards HH 212 using the ASTE telescope. Our observations with a 22”-diameter beam show that the SiO emission is highly concentrated within 1’ of the driving source. We carefully compare the SiO observations with archival H2 1-0 S(1) images and published H2 echelle spectra. We find that, although the SiO velocities closely match the radial velocities seen in H2, the distribution of H2 and SiO emission differ markedly. We attribute the latter to the different excitation conditions required for H2 and SiO emission, particularly the higher critical density (nH2 ∼ 10 8 cm) of the SiO J=8-7 emission. The kinematic similarities imply that the H2 and SiO are associated with the same internal working surfaces. We conclude that the SiO J=8-7 emission has a potential to probe the jet/wind launching region through interferometric observations in the future, particularly for the youngest, most deeply embedded protostars where IR observations are not possible.