The jet/counterjet symmetry of the HH 212 outflow

Abstract

We present Spitzer (IRAC) images and a VLT 2.1 μm image of the HH 212 outow. We find that this outow has a strong symmetry, with jet/counterjet knot pairs with Δx < 1" position offsets. We deduce that the jet/counterjet knots are ejected with time differences Δτ0 ≈ 6 yr and velocity differences Δv0 ≈ 2 km s-1. We also analyze the deviations of the knot positions perpendicular to the outow axis, and interpret them in terms of a binary orbital motion of the outow source. Through this model, we deduce a ≈ 0.7 M⊙ mass for the outow source, and a separation of ≈ 80 AU between the components of the binary (assuming equal masses for the two components). Finally, using the IRAC data and the VLT 2.1 μm image we measure the proper motion velocities, obtaining values from 50 to 170 km s-1,.